So, lately I've had a problem that comes and goes. At 6-6500rpm (varies slightly) the engine some times cuts hard. The engine is of course warm (driven at least 15-20 minutes in 20*C/68*F). Oil level is full, and oil and filter are new. Engine is freshly rebuilt to stock specifications in all clearences etc. Engine has about 600 miles now, but oil and filter was changed after a few start-ups and 200 miles.
I removed and cleaned VTEC solenoid to and MAP sensor to be sure, but still the same problem. It doesn't happen all the time, but has happened 3 or 4 times the last 2 days. If it happens on a pull, it can be all good a minute later on the same drive. I can also rev freely past the cutting point. The CEL blink for a split second when it cuts, but it doesn't leave a code.
Stock ECU and engine harness.

Any suggestions?