Re: Rpm and acceleration trouble
Welcome to the garage.
When the engine speed reduces to 1500 rpm, the vehicle also reduces speed?
It can not be in limp mode, because the rpm should increase then, besides the fact that a P0700 and probably a more specific code will be set.
How is the idle rpm? Should be at 650, but when higher, could cause a bang when shifting from R to D. Also play on a U joint can cause a bang.
Do you have a scanner with live data? It would be nice to see what the TPS % is doing when pressing the accelerator. Also the MAP (manifold air pressure) should be checked, as it is the #1 input for fuel injection. Does the engine start without problems?
Checking fuel pressure and cylinder compression would also be on my list.
Also check for a vacuum leak, since you have the P0455 code.