Cm870 running like it out of fuel???

[Rtrucking]

Ok so I know it's been a bit but I'm going to give a update on the truck, just replaced the ECM this last weekend and had running rough program it, his program is great and it ran good for the little test I did BUT now it's doing the same damn thing it did before but even worst now I can't drive it more then 30ish minutes and I have to pull over just like it running out of fuel I'm at a lost and look for ideas on what I need to do next, fuel pressure will be 280ish then drop to 210 and falling to 110ish then I stop and shut off the engine and check things out and can't find anything wrong then it starts running better then does it all over again.