X2 on the tranny possibility. I'd look at the converter pretty close also.
I'm not too afraid of the timeing your running but the jetting has to be there also. Might try backing it off to 35° or so. But I'd bet if the jetting is correct then you might even like a few degrees higher. Is the distributor locked out? If not then what the initial? When is the timing all in by?
Is this a MSD system? If so....is the are you running a charging system and is it operating properly? Is the battery properly charged? Are you sure the pickup wires going from the distributor to the MSD box have the correct polerity? Are you running a 2 or 3 step? If so,...have you tried to change the chips around a bit?
Fuel system could be the culprit,...but it could be a low float level, kinked line, or some other kind of restriction in the fuel line. What kind of scoop are you running? Is it set up correctly? This could be speed related which could be air delivery....
Just some things to think about.
Don