sometimes I have to keep rpms at 1000 to keep truck running (ambient temp has no bearing on this problem)

 

Sounds like you could have an or several injectors starting to get out of spec for there fuel delivery. Have them POP tested with the idea that you will likely have to know who's injectors you want to replace them? I wanted the dollarshop the POP test them and they didn't figure it was nessecary because of the EGT was about the same, they did test at 2600 PSI to 4100 psi at a different dollarshop. I went with the 300's on the 3rd go round.