Have A 2000 2500 , New Lift Pump , Rebuilt IP, Maintains pressure at outlet side of filter housing ,Runs GOOD until Hot Then Surges Worse and Worse Until Dies Will start back up but runs bad untill cools off! Does Anyone Know What The Fuel Temp Reading from the pump Should Be...

 

If it's messing up when it gets hot, I'd suspect the Rebuilt Injection pump.
The major rebuilders of the pumps use the newer "FedEX" electronics that use beefier heat and vibration isolation.
Who did your pump?
Is it raw aluminum colored, or painted black?
The black ones were rebuilt overseas (IIRC) are cheaper and have been problematic.

 

If you ran it until it started running poorly and have access to the cummins test tool most dealers have that will eliminate the ecm and wiring.

 

I just wanted to add to what Ed said, some but not all black pump are made overseas. The black beauty AKA "Czech" pump are the ones to look for. My rebuilt pump was black, but made in the USA.