2001 Chevy Blazer 4.3 Vortec "w" engine code

Ok this truck has me frustrated beyond belief.
Here are the symptoms
Runs normal at idle
When throttle opens it acts like its missing and starts to putter like its going to die out
It also backfires when you get the rpms high enough

Fuel pressure is at 60psi with key on, holds at 52-54 with key on pump off. Drops to the low 40's after ten minutes. Holds steady at around 53-55 when running.

There are no misfire codes.
The only code that i have is a crankshaft position sensor malfunction code.

Have replaced the distributor
Have replaced the fuel pressure regulator.
The injectors all read the correct ohms when tested.
When i pour gas through the throttle body the truck will run fine at high rpms. But my fuel pressure is to spec. The only thing that im unsure of is the pressure dropping after ten minutes. Could i have a leakdown somewhere?
Any help would be greatly appreciated!

 

a malfunctioning crank sensor can cause your problem..have you replaced it?