1985 Camaro not enough power

85 Camro Iroc, 305 TPI.
350 heads completely rebuilt and installed. The transmision completely rebuilt, including torgue convertor.
Vehicle timing computer set by local garage.
New gas tank, new fuel pump fuel and filter. The fuel has been treated for injector cleaning(seafoam).
But the engine appears to be sluggish when punching down on the gas from a dead stop.
It just appears it should have more power or get up and go.
I also hear an occasional backfire, once in a while the check engine light comes on but goes away. But the car appears to run smoothly, idles good and has never stalled on me.
Can anyone please give me some ideas on what I can check next?
I appreciate any help.

The 305 TPI had 58cc heads, the 350 heads (unless they are corvette alum heads) are 64cc-76cc. you have effectivly lowered your compression greatly. Not to mention that IF the valves on the 350 heads aren't hitting the cylinder bores they ARE severely shrouded (intake) and not flowing like they should/could.

Are you telling me that the mechanic that recommended the replacement heads(350) didn't know what he was doing and effectively screwed me and I will never have the power I am suppose to have with this engine?

put it this way, if it is a 305 and you have 350 heads on it, you are screwed! your valves are probly done not to mention the top of your pistons.

Since you have lowered the compression by putting on those 350 heads you COULD find a way to install either a supercharger or a turbo setup and that will give you back your performance and then some. But it will probably be expensive, I would go back and talk to that mechanic and explain that you are dissatisfied and that his advice was completely wrong. You could try to get some money from him but I doubt you will. Good Luck.