Rev drop or not - ECU issue?

I have a Honda K20Z in my car (an Ariel Atom 2 NA) - stock engine except for reinforced rods and pistons. I was just cruising on the highway (on my way to the race track), when all of a sudden while doing 110KPH (68MPH) the revs drop and pick up again in a jolt and redrop. There after if i passed 4 KRPMs in 6th gear or 3KRPMS in 5th (same speed), the engine drop.

If I gently accelerate it will work past the 4KRPMs unless i went down the throttle a bit. If i accelerate the usual way (brutally in an atom :)), the rpms drop again.

If i rev with no gear engaged, no problem. If i downshift or clutch+rev over the speed of the drop-mark, the engine will continue.

Is this an ECU issue as im told? It worked fine for 2 years and about 2000 Kms (1250miles). I had a similar issue when the TPS (throttle position sensor) went bust but then the accelerator never worked past idle...

Ideas of possible causes: TPS (not completely broken), fuel pump, injectors, bad contact somewhere?

What can i check? TIA!