Who wants to play detective? 2008 Tundra 5.7 AB60F

Hello all! First time poster here but long time Toyota owner. I'm hoping someone can help with a mystery issue I'm having with my 08 5.7 Tundra 6 speed auto.
Here's the story:
Bought my truck about a year ago with almost 250k miles but no power train or drive train issues. I intended to only use her for light duty and 1 road trip a year so the miles don't scare me. Unfortunately I started have a rare but recurring issues where the engine and trans would go into "limp mode", limiting the rpm to under 3k, but I would go away after warming up, restarting or playing with the trans. No codes were thrown when the truck would do this. Eventually these events got more frequent and finally registered check engine codes C1201(engine control system malfunction) and P2757 (TCC Solenoid press Ctrl sol Ctrl ckt perf/stuck off). After time and research I replaced the TCC or SLU solenoid inside the trans. However the replacement solenoid was not a vin matching part but was identical in form and did seem to fix the issue. It didn't last long though. Within a 2-3 week period I realized the truck would need warmed up to temp before it would operate normally. Otherwise it would be weak or in limp mode. At the end of that period she went right back the same limp mode state but wouldn't register any codes. That brings us to current day. I've had a trusted transmission shop inspect the trans but they sware the trans is fine and claim that the issue is something limiting the engine and trans. They suggested the TPS could be bad. I've been to a dealership and they claim that the torque converter is failing and I should just replace the trans.

Here are some symptoms:
Engine and trans run fine. No unusual noise or vibration
While in park or neutral the engine will respond to throttle input correctly but while in drive something limits rpm and the engine won't respond correctly to throttle input. If you push the gas past a curtain point and throttle response becomes non-existent until you floor it. Then the truck downshift to compensate for lack of rpm (aforementioned "limp mode")
Only have access to gears 1-4 (5 according to the trans shop)
Reverse, 4low and 4high all still work
Codes C1201 and P2757 appeared once but haven't returned after clearing. Truck won't throw codes.
In this state she can't do highway speeds and can barely do 45-50 especially with hills

At this point I'm searching for theories to chase and insight. Currently my options are replace the TCC solenoid again, Chase the throttle response theory or go full ham and pull the trans to replace the torque converter or replace the trans. None of which sound like silver bullet options so if anyone has any other ideas I'll take what I can get. Thank you!!

 

Dealer will always want to just replace the trans if there seems to be any issue cause they aren’t trained or don’t want to spend the time fixing it. I’ve heard that sometimes there are hidden codes that normal readers can’t see and you need Techstream to find. Did the dealer mention any other codes besides the ones you saw?

I had some of the same symptoms but was under warranty and the dealer just replaced my transmission.

 

Yeah I know the dealerships MO haha. The tech mentioned "hidden codes" for the torque converter but symptoms for a failing TC don't really line up with what's going on.

 

If you have a basic code reader, take it to a local auto parts store and have them run a full diagnostics..

 

You might try replacing the speed sensors on the tranny. There are two and they are fairly cheap at about $50 each. If I recall correctly one is for the tailshaft speed and the other is for the torque converter speed. They are literally a five minute, one bolt job. Unbolt old sensor, bolt in new sensor. Easy access on side of tranny. Bad speed sensors can cause just the kind of havoc you are experiencing.

 

P2757 FIXED - Toyota Tundra Forum


Also:

According to the service manual, P2757 is related to the torque converter lockup in the AB60F transmission. The description isn't all that clear.

DTC P2757, P2759: Shift Solenoid Valve SLU
During a solenoid valve SLU malfunction, the current to the solenoid valve is stopped. This stops lock-up control and flex lock-up control, and fuel economy decreases.

P2757 Torque Converter Clutch
Pressure Control Solenoid
Performance (Shift
Solenoid Valve SLU)
* Shift solenoid valve SLU remains open or closed
* Valve body is blocked
* Torque converter clutch
* Automatic transmission (clutch, brake, gear, etc.)
* Line pressure is too low

 

Something else to keep in mind on these shift solenoids and such is that they are all obviously connected electronically, so in addition to the solenoid itself being bad, you could be experiencing a wiring/connectivity issue as well. It may be worth examining your connections for signs of corrosion, being loose or damaged; wires, those tiny pins, etc.. can all be culprits and they are not easy to track down.

Also, only having gears 1-4 is consistent w/the vehicle entering 'limp mode' and the C1201 code is sympathetic to the original CEL code and is what forces the truck into limp mode.

When you do put a code reader to it, make sure you are having it read 'all available codes' and not just 'check engine light codes' or 'common dash light codes'. There's a chance that the original 2757 code is cleared now (whether permanent or temporary) and the C1201 (limp mode) is still active in the background.

In other words, when the truck originally went into limp mode, you should have had a CEL, 4LO flashing, VSC and traction control warning indicators all flashing (may be one or two others). If you were to successfully clear the original 2757 code (but not independently clear the C1201), you'd probably see the CEL turn off and the flashing 4LO turn off but you'd still have the VSC and traction control indicators flashing/on; and at this point the truck would only be able to shift within 1st - 4th gears (still in limp mode). Once you clear independently clear the C1201, you should have all 6 gears unless you truly have a mechanical problem that will not allow the vehicle to shift beyond 4th...

With all that being said, if the original cause of the 2757 code is not truly remedied, then you'll repeat the cycle and the truck will eventually end up back in limp mode (may be immediate, may take a couple of days, may go for a month or two)...

I wish I had something a bit more definitive for you, but if nothing else I hope this helps you understand what's happening w/the codes and the presence of limp mode. A little extra info may also help you provide something to your techs that points them in the right direction as they try to help you resolve.

Good luck on a quick fix and hopefully not too costly fix

 

These trans are starting to become Legendary for how well they are built. I've have 2 Tundras now, an 07 with 485k and now a 12 with 356k, no major repairs to either yet.
Start with the fluid, drain and fill the trans a couple times with OEM WS.
Clean the throttle body and MAF. My 07 would hard start because the throttle body was disgusting.
I've also had a 2000 4Runner in between these trucks, had lean codes on both banks and it was a bad O2, no O2 codes but scan data showed the upstream wasn't switching like it should.
What's the service history like on this 250k truck?
If the trans fluid wasn't changed regularly and the truck was actually used as a truck the trans could have significant wear already and actually be failing.