Tachometer and voltage gauge off?

05 double cab

was out hunting yesterday, no more than 3000 ft elevation.
Got back in truck to start heading home, hit the main road and realized that when coming to a stop my tach have would be resting at 0 then while under load it would still be reading lower than it should. Also noticed my voltage gauge/meter was being a little jumpy. Waited til I got home to shut it off and restart it. After a shut down and restart it was fine. This morning was fine as well, after I fueled up I noticed it doing these same things again.

voltage out of battery is correct, and connections are all nice and tight.
Anyone seen this before or have any feasible ideas on where to start.

 

Hello and welcome!

I am sure someone else with more expertise will come along

In my experience,many unexplained electrical things can be traced back to a faulty battery.

I would have it load tested,which can be done at a parts store for free.

It may have a bad cell or two which can trick you.

Also it wouldn’t hurt to chhexk your air filter condition,and also clean your MAF Mass Air Flow Sensor while you’re in there.

ONLY use MAF sensor cleaner,don’t use brake cleaner or anything like that.

 

Put new battery in, voltage gauge was fine for awhile, went out hunting deep behind Weyerhauser gate walked back to truck after calling, came back to truck and nothing no juice anywhere. Smacked the battery and got power back, drove immediately to get out of the gate. Voltage gauge was bouncing bad at this point. Then once outside the gate. It does it again. Nothing. Walked to get cell service, wife is now on way with jump box and tool bag. Cleaned positive cables and it fires right up, did have a 30 amp fuse blown for battery charge in same box as the trailer brake shit.
Go get battery tested and bad, literally only a month old. Got another new one in and voltage gauge is fine.

now it is just the tach, after a little driving it will drop to 250-0 rpms. Shut it off and fire up again and it back to normal. What on earth could be causing this? It’s driving me nuts, so much so I’ve been driving the Honda instead of the truck.