After vehicle has been setting and turn on the key the gauges don't read correctly. They all read low. Once truck is warmed up and shut off and restarted, the gauges read correctly. Any ideas?

 

Possible pigtail issue, or body control module maybe, just a wild guess.

 

2001 guages are always flakey, IDK. after an overhaul i would expect it to do that 1st time and ignore it?

Always insure battery is good first. Insure there are no parasitic leaks.

* insure key on/off is doing it's work (work it carefully to insure it makes contact it should)

* fuses are for pulling. isolate off un-necessary things by pulling fuses, see if that helps.

* the wiring box near the gas pedal may have poor grounding. it is wired quickly by hand.