kleinjesse

I have a 2000 Silverado 1500 Z71 4WD. About 6 months ago the original motor gave up and I installed a Class 1 Jasper 5.3L. I have put about 9000 miles on this new motor and have been experiencing the same problems since installation.

Sometimes the motor runs amazing, but most of the times it is so sluggish, lots of hesitation. There is almost no throttle response under 3000 rpms. If I push the pedal down to the floor, it down shifts, makes a lot of noise, but does not accelerate as it should. The old motor had this same problem, but with 250,000 miles, I thought it was just worn out and had given up. Apparently not the case.

Here is what has been done to attempt to fix the problem:

New intake gasket
New knock sensor
New crank sensor
New throttle position sensor
New mass air flow sensor
New b1s1 02 sensor
New fuel pump
New fuel filter
Rebuilt rear end due to destroyed spider gears
Injectors cleaned and flow tested within spec
Cat. Converter back pressure tested and passed
Tested a used ECU from the exact same truck
OBDII throws abosolutely no codes
Chevrolet dealership diagnostics report nothing strange or out of spec
Transmission has been checked, non intrusively, no problems suspected
Have driven an identitcal truck, drives as expected, not sluggish

The only other problems I have with this truck is when I go to pump fuel. I have to pump VERY VERY SLOWLY of the filler neck will over flow and it will cut the pump off. We are talking 15+ minutes to go from Empty to Full. This is very annoying, I doubt the problems are related, but figured I would disclose this issue as well.

Any help on either issue would be greatly appreciated. If you need any more information just let me know.