So I have a 2001 Blazer. My Check engine light starts flashing only while I'm in the middle of driving. When I slow down or come to a stop, the CEL turns off. I've replaced the crank/camshaft, got the crankshaft relearn, did all my vacuum lines, and now I'm stumped. I'm not sure what could be causing the misfire only while I'm driving around 55 for a bit. I've left it to idle for a while, no light. Revved up the engine, no light. Any tips would be great.

 

Fuel pressure test? Maybe after turning RPMs for a while you're loosing fuel pressure? Could juts be an old filter, could be the pump on the way out.

But I'm just throwing out ideas. Fuel filter is a cheap and easy place to start.