A year ago I took my stock 95 Chevy truck 350 and stroked it out to a 383. I upgraded to a 670cfm Holley throttle body to handle the extra flow and fuel. I have tried custom chips from both Jet and FAST. Neither company could get the engine running properly. My major problem is that the timing retards below 0 degress during shifts which causes fire to shoot from the intake. These timing retards are only during shifts at wide open throttle. If I don't smash the petal to the floor the timing doesn't retard so much that I have fire comes through the intake during shifts. Also the motor just doesn't want to accelerate very well. If you were wondering the vacuum seems to be good all the time. I am not throwing any check engine codes. I also use Datamaster logging software to watch all my engine parameters. I am up for any ideas that anyone may have for me.