93 5.2L JGC backfires at around 2000 RPM

1993 JGC 5.2L Will miss and backfire cruising at highway speeds, to date I have changed TPS, Dist cap & rotor, plugs and wires, flushed injectors, crank position sensor, cam position sensor, temp sensor and I still have the same problem as when I started. Could the Idle control motor cause this problem it surges a little at idle but I have not removed this part yet.

I bought this thing cheap but if I do not find the answer soon it's going to get expensive.(divorce):grinyes: I miss the days of no computers just raw horsepower.

If any one out there can help please let me know.