Hard Start, Fixed HPOP leak, still runs bad

[jamsnoop]

I have an 05 6.0 and it started to run rough when cold and then one day would not start. Took to dealer and they told me some seal or something was out on the HPOP. I just fixed it and did not replace pump because I just wanted to sell truck. Even after I got it fixed it starts but still runs real bad when cold. I basically can not start the truck unless it is plugged in if I have shut it off over 3 hrs.
I had a friend put a scanner on it and he thought it was probably a weak pump it was reading 580 when ideling and when you steped on the gas it did not really go up but when you let off the gas it would spike for a second. There is sparatic codes for injectors but not always. mostly only after you step on it and then let off it then threw a code on several. I am looking to tear into this to try to make it more bullet proof and maybe doing a delete and tuner but not really convinced that this HPOP would be the cause of the hard starts. Any ideas I am ready to spend the money but don't just want to replace parts etc and still end up not fixing the issues. It has 130k and I have never really done anything to it nor have I tried Rev-x. I pulled egr a few mos ago but really looked pretty clean. Thanks for the Help!