I too have been struggling for some time with low speed hesitation on my 95 Z28 and it has been throwing no codes at all. I am an LT1 Edit and Datamaster user and have revised the program at least 100 times or so. Here is my setup: 4L60E, 3:23 gear, 355 blueprinted block, stock crank and rods, forged pistons floating pins,10.8 compression, ported stock heads, stock cam, CAI, Tbyrne MAF ends, Trickflow elbow, BBK52mm, 32lb injectors, taylor wires, and the noise makers... 1.6RR, Edelbrock headers, Random Tech CAT, Edelbrock cat back.

I had to high load, low RPM stumble at part throttle, like going up a hill in high gear and the A/C made it worse. It pulled timing, popped....you know the story. Pulling timing out of the left lower quadrant of the timing table didn't help any.

Two things: I found the PCM ground loose and why the factory bolts it on the fender over paint is beyond me, but I removed the paint, added dielectric grease and reinstalled it........and it still knocked/stumbled.

So I removed the LT4 knock module and reinstalled the original LT1 knock module (yea LT4 KM out, LT1 KM in) and the freakin knock curve went flat....no knock, nada, zero, no stumble......I tried to make it stumble.....nope, no knock no stumble.......knock curve was flat....knock counts did not move.

Being excited, I reloaded the stock timing table........killer!! No knock......

SO:
1. Either the LT4KM went bad or is not compatible on OBD1 or both.
2. I was surprised not to see knock with the LT1 KM with RR and headers.

Go figure......

REPLACE THE KNOCK MODULE......

Hope this helps somebody out there. Many other things cause stumbling too, but when you have replaced everything else unsuccessfully, try a new KM.....