96 Turbo Cummins idles fine when driving around town but after a run at freeway speeds when it idles down it stalls out from to low an idle.
If I shift into neutral when I come to a stop a few times it seems to be ready to idle again.
I think It's likely to be a pump problem but I'm not sure if it's the transfer pump starving the injector pump or a faulty injector pump.

I have run into a couple of cases where the torque conveter clutch "sticks" and kills the motor when you slow down. Kind of like forgetting to press the clutch on a std transmission. See if you can disconnect it and try it.

I have no idea how to go about that. I did have a heavy duty torque converter installed about 30,000 miles ago by Aamco along with a shift kit and a few other upgrades Dodge recomended during a rebuild.

I can't help you on how to unhook it on your truck. Maybe someone else here can post. I'm sure the dealer could do it but doubt they will tell you how. My mom's new car developed a transmission shudder every now and then. She took it to the dealer 6 times and the last time they said they finally fixed it. I bought it off of her years later and while checking it out I found the torque converter clutch wire cut. What a great dealer. It only gains you about 1 MPG so I never fixed it. On her car it was a wire that went directly into the bell housing.

If it tries to keep pulling while killing the motor then a stuck torque converter clutch is suspect. If it's just trying to die, it may be something in the injector pump.