The heads are actually a set of 1.94"'s from a TBI truck. The distributor is an older GM HEI upgraded with Accel parts (cap, rotor, coil, wires). The exhaust is 2.5" y-pipe to 3" gutted cat and 3" all the way back to the Flowmaster. Also, the carb is an edelbrock 600cfm, mech. sec., and elec. choke.
Now that I have straightened this out a little, hopefully you guys can help a little more.

 

Sorry, but there's really not a lot we can do if you can't find something out of line, we can't magically guess what is wrong. Hell, don't make me use my rear defroster gremlin theory again...
All i can say is this. First are you sure it's really as slow as you think. If you aren't running it at the strip/g-tech/racing against someone with known timeslips then you are trying to guess how fast it is SOTP. That's a pure crapshoot. I've been in high 14 second cars that felt like rockets and had my own high 13 second car feel sluggish sometimes.
Other than that, there is a lot more to your combo then just the engine A tigh converter (such as stock) and tall gears will seriously stifle a modded motor. You describe your cam as mild, well what does that mean. If it's over 220' @ .050 and you're pushing 2.73s and a stock converter then no doubt it's a slug. Hell, any engine will feel like a slug with 2.73s.
But then there's always other issues. Perhaps you have a weak spark or your timing is all wrong. Maybe that truck 350 has low 8:1 compression and combined with the aforementioned cam/gears/etc it has no umph left. Perhaps those TBI truck heads are swirl port, completely choking you for power, further compounding the low compression/over-cammed/under geared problem. Or maybe when you put it together one of the gaskets is mis-aligned/slipped and you have an intake or exhaust port that is half blocked. Or any other combination of tuning issues with any of this.
hope that gives you some idea of the generality of your post...ed