I had that, well fairly similar, was a tps, missing a tiny spot, tested 100% perfect, could not find a low/missing resistance on it anywhere, but was there just above idle on throttle and low engine speed.
When I changed ecu's, the fault became massively amplified to the extent that it couldn't even be driven through in a higher gear on the rollers, so had to put on a universal one, then perfect.
I was stunned by the difference it made on the new ecu, the L6 coped much better no doubt by overfuelling all the time.
tabetha