05 Tundra over drive not engaging

Hello I am a new member here. My truck is a 05 Tundra crew cab. It’s on a 6 inch suspension lift and 2 inch body lift running 37 inch tires. I am having an issue where the transmission has a hard time shifting in OD with out a little help. I either have to press the tow button twice to get it to shift into OD or when I’m up to speed I have to let off the gas or very lightly be on it for the transmission to shift into OD gear. Besides that it does shift very smooth. Fresh fluid has been added and I am running a temp guage it stays at 150F in normal driving condition and hovers to a bout 180F when towing. I purchased the truck a few months ago and has always done this but it is an annoyance. Previous owner states it’s because of tire size but I doubt it. Any suggestions would be appreciated!

 

Hope someone here can help you with this issue.

 

It shifts on a speed/load curve. Its not inconceivable that both values would be skewed with 37's. At fully closed throttle it should up shift @ about 43 mph. How far will your 37's roll with a fully closed throttle? As throttle increaases the minimum speed required to upshift increases. At full open it shifts at about 105 mph. So if it doesn't shift by 115 mph it probably is broken.

 

@ blue trucks

If that is accurate then it very may well be that the tire size is messing with the shift point. As mentioned if I let off throttle at around 35-45 mph it will shift into OD or by simply using the OD button when it’s up to speed at any rpm. Being that it shifts smoothly through every gear and does not slip I don’t think my transmission has any internal issues I was leaning maybe towards and electrical problem. Thank you for your input and any one else is welcome to chime in.

 

I was hoping for a report on the 115mph test.

 

Haha that there is a death wish in my behemoth of a truck you’ll have to try that experiment on your own

 

Speaking of behemoth, with 15" of additional height your wind drag alone will require more throttle. Moving your shiftpoint further up the scale.

 

We need pics!

 

Good point. I do wish there was a way to flash the ecu and calibrate the speedos on these trucks.

 

Are you running stock gears in your diff(s)?

 

I’d tend to listen to the prior owners reasoning on this one.

 

Not gonna claim that it is accurate. It is my best translation of the FSM transmission diagnostic page.

They call it "throttle valve" and it only references the fully closed and fully open positions. They don't list a table of potential combinations to engage 5th. And I correlated that with the fact that my butt sensor believes my shift points vary on my 4sp, yet they clearly occur when driving conditions are neither full open or full closed.

 

This is the only question that matters.

 

Welcome from Vegas....
Nice truck.

 

The tires have drastically reduced your gearing and the lift is adding major aerodynamic drag.

Your transmission is reacting as it should to the added load.