Check engine light flashing

[bikernut]

I have a 2003 GMC 3500 4x4 with a 6.0 engine. Problem: when plowing snow, hauling a small Kubota tractor or just driving down the road when the engine RPM gets to about 2200-3000 the check engine light starts flashing, I let off and reduce RPM and it stops flashing. What I have done so far is replaced the knock sensors 2 times, changed all 8 coil packs, 8 spark plug wires and 8 spark plugs all GM products no aftermarket stuff. I have gone to the local service station and had the scanner installed and driven it to the RPM and it says misfire in about 4 cylinders. When the light flashes it won't set a code just flashes and this is about to drive my crazy. The engine idles nice and smooth and when the light starts flashing at the RPM there is no roughness to the engine at all. Anyone have any ideas?? I have even gone and disconnected both batteries for a 24 hour period. Do I need to go to the GM Dealership and have the computer erased or re-flashed?? I'm at a loss, truck only has 45,000 miles.