Misfire 5.7 Vortec

[cjauto]

Recently purchased a 99 K1500 Xcab SB 5.7 Vortec Automatic from a good friend. He only owned for 1 year and had this problem happen once. In the last 6 months the truck has had a new fuel pump, plugs and wires, vent solenoid for evap. The truck has 133k miles but runs strong. I've put on 800 miles and this problem has happened 3 times. So heres the problem.... randomly while driving the truck it will begin to misfire almost to the point it will stall. The first 2 times it would idle fine and only happen if I touched the gas pedal, and would continue till the truck was shut off. Restart few minutes later and it would be fine. This 3rd time the problem seemed worse. It started after 5 minutes of city driving. Truck was shut off for 10 minutes. Restarted and drove another 10 minutes with problem still occurring. Shut truck off for about 2 hrs and the problem was gone. This morning driving to work it seemed fine too. It seems to only happen at 1/4 tank or less. It has never tripped SES. It did have code po171 (I think rich bank 1) I'll have to scan it again. The only other thing i've noticed is that the oil press gauge has an elec flutter like a bad sending unit. When the problem happened yesterday it almost looked like when the engine missed I could see the oil gauge drop like an electrical short. I rely on this truck everday and need the prob fixed asap. Any help or info would be greatly appreciated