96 Tahoe P0300 Code-random Msfire

[nymiskovics]

Looking for some help. Have a 96 tahoe giving me issues. Was running fine saturday morning, left running in driveway, after about 20 minutes, I drove down road, started chugging, and MIL light came on. Shows code p0300. Clear code and it is back within two minutes. Flashes showing sever issue. Backfires at all rpm ranges. Have replaced all four HO2S within the last month in oreder to pass NYS inspection. converters are about 2 1/2 years old. replaced injection spider, plugs, wires. checked EGR, IAC, MAP. Rebuilt engine in July. Has 170lbs compression on all cylinders. re-adjusted all rockers. When I take off the upper intake, the inside is wet from fuel on the rear half of it. Fuel pressure is 60lbs. No fuel leaks. No bent push rods, inspection of valve movement shows no signd of wear on cam. I am stumped. Anyone have similar issue????? I have disconnected all H02S to eliminate computer compensating any fuel, and it runs slightly better, but still cannot drive without making exhaust cherry red.