Truck will not shift into gear unless it is pretty warmed up

Hello,

This sounds like you have a clutch disc that is falling apart or the pilot bearing is seizing up.

Here is a couple of guides showing you what you are in for when fixing the car:

https://www.2carpros.com/articles/how-to-replace-a-clutch

and

https://www.2carpros.com/articles/pilot-bearing-replacement

and

https://www.2carpros.com/articles/clutch-doesnt-work-sometimes-or-not-at-all

Please let us know what you find. We are interested to see what it is.

Cheers, Ken