my gues would be the following things:
1- afr is leaning out at a certain rpm
2- tps sensor is acting funny,check that with a meter.
3- map sensor is acting funny,check that with a mter.
if you have an fpr then check if your pressure is holding fine or not,increase the fpr pressure to 70psi and see if its hold,if it doesnt hold it there and is fluctuating then it can be either a fuel pump issue or a block fuel filter aswell.