Put a new 355 in my shortbox ('83 C-15 w/ SM465). Motor has vortec heads, Edelbrock Performer intake and a comp cam (.447/.462 210/218 111 seperation). I'm still running the Q-Jet. If I really drop the hammer to go fast, the truck throws you back like it should, then bogs for a sec or two and then gets with it again. It'll do the same thing about no matter where I have my timing set (have all the adjustable crap, vac advance is running full manifold). It doesn't seem to care what speed I have the motor turning, just when you really press the throttle in.