1999 GMC Sierra Engine misfires

Hello I wrote in and made a small donation and had the question:
Engine Performance problem
1999 GMC Sierra V8 Four Wheel Drive

Automatic 207100 miles

My truck

misses under a load, does not Miss at idle, I have varified that it is the #8 cylinder that is miss firing. I have checked the fire from the plug and wire and both are good, fuel pressure is good and I switched the injectors and coil packs from a known good cylinder to the #8 cylinder and it continues to miss fire under a load, I also just replaced a bad fuel pump and filter, when I replaced these that's when this problem started, it ran fine before the fuel pump went bad.I am out of option and don't know what else it could be, thank you for any insight.
And the solution gave was:

Have a look at the PCM ground at the back of right side cylinder head, there is a tech bulliten on it, I will email it to you

i recieved the bulliten and checked the pcm ground, it was a little dirty but nothing out of the ordinary, I cleaned it and put it back on and did not solve the problem, it still misses. Do you have any other ideas. The only thing I can think of is that there is a problem between the injector or coil pack and what ever controls them. Because like I said I switched a good coilpack and injector from a known good firing cylinder to the #8 which is miss firing and it still misfires. So im thinking whatever tells the injector to spray or the coil to fire is bad. But u guys are the pros. What do you think? Please any advice is greatly appriciated. Thank you

ERic

Ok ill try that, I did a compression check and all cylinders came back in specification

Well I tried spraying the gum out to check for vaccum leaks, there wasnt no change in the idle.I soak downt all the vaccum lines I could see.