Well here it's I have a 97 5.7L Vortec in my Isuzu cab over. It was running rough so I check the timing and it was -22* so I clocked the distributor and it sounded and drove way better. The very next day I was at a stop light and all a sudden it started shaking and it hardly got me to the job site. I was able to get it home and I changed the distributor, cap, wire, plugs, coil, ECM, and the timing chain. She fired right up and still out -22*. I hooked it up to a smart scanner and revved the engine above 1000 RPMS and turned the cap to smooth out the timing. It would jump from 13 to 19 to 21 all over the board hunting around. There is not that much play to bring it down. So I turned the distributor back 1 tooth and it wouldn’t start then 1 tooth forward and it was -30* out.