Update.

Jeff replaced the knock module with one for an LT4.

He also (last couple days) has had the problem get worse, to the point it wouldn't idle at all. Running very rich. He replace both 02 sensors and replace the exhaust collector donuts by the 02 sensors with new ones. Took it out for a test and it runs much better but still not like it should. It still has a hesitation off the line. He still hasn't bought a fuel pressure gauge, that will probably be next on his list. Anytime I've had a lean condition it's been at high rpms, this happens at low rpms and straightens out at high rpms. In higher gears when the engine is lugging harder it has all the fuel it needs and pulls hard like it should.

Any other ideas? Jeff's gettin' frazzled.