My son has a 1996 Suburban Tahoe 4WD 5.7l with over 200k on it. Several weeks ago we had to replace the intake gaskets because of a coolant leak and I noticed then that his truck was sputtering or not hitting on all cylinders. Even after replacing the cap, rotor, wires, and plugs since we didn't know when the previous owner last did it, it still runs like crap. We did reinstall the distributor to the marks we made after working on the intake gaskets but never put it on a live data display to see if the distributor is within a +2 to -2 range. I don't think that would have anything to do with a P304 code he has now though. We took out the #4 plug and it was fouled black like it hadn't been firing. I've read about crappy injectors for those year engines and maybe the possibility of a valve issue. Anyone out there have any suggestions? Thanks

Yep, those crappy poppet injectors are known for leaking. Upgrade to the newer style injectors.

I that there are reman injector kits, but you can't really trust this style of injector especially after a rebuild.

Go with this style.
GP Sorensen Fuel Injector 800-1513N - Read 3 Reviews on GP Sorensen #800-1513N