Cumins isx 15 NEED HELP AND ADVISE

[Kenworth t660]

I have not taken the head of and it will cost 5 k and i dont want to do that right now . My main concerns i want to address is the fuel pump and the delete programing to have it programed right . . Im gonna have the fuel pump checked pressure tested and opened to inspect inside . My driver checked and had no particles in the fuel filter and he told me that the truck today took hills doing70- 75 like nothing and it was loaded 15 k . Im gonna have pump opened and checked and i will also have it rebuild but just wondering why some shops says its not good to rebuilt pump with aftermarket parts And instead should replace ??? I will have motor inspected/ pump inspected/ and check the computer to see whats going on with programing . Please tell me if i am going the right direction??