Just bought a 97 and the temp only comes up a little on the guage no where near the middle 90 mark like my 02 does , the pre owner says its correct. Where does your needle rest at when fully warmed up????Thanks

 

A good flush job is probably in store and change out the thermostat when doing so, some thermostats just don't last long. The needle will not rest anywhere if you are just running around and no load is being put on the truck as it will fluctuate like most do. Goodluck,,, Rick

 

Mine usually runs at about 150F but will climb to about 180 then go back down.
This is considered normal for a 12 valve.
It is very common on these thermostats for the internal rubber sealing ring to come off and keep the stat from closing, engine runs too cool.
I've always just removed the ring and trashed it, seems to cure the problem with no ill effects.