sputtering, coughing, backfire

Man Oh Man am I getting frustrated here.
Engine still sputters, coughs with an occasional backfire starting right around 1900 rpms and up. Don't matter what speed. Didn't have this problem before the rebuild. It runs really smooth under 1900 rpms.
checked all the vaccum lines, replaced crank position sensor, has a new ignition module. Could the distributor be a tooth off? If so would't run crappy all the time? I had in a shop a couple of times and they could not find it. The occasional backfire part leads me to believe a timeing issue, but it runs good at anything under 1900 rpms.
What would be my next step? I really appreciate as i have been able to solve a lot of other problems just reading the forums. Thanks guys.

I would definitely check the distributor indexing first. If it is retarded by one tooth it will start and idle beautifully, even unusually smoothly, but will backfire, sputter, and not rev. If it is advanced one tooth, it will start badly but run well. I don't think it will start or run at all more than a tooth off. Guess how I know this?

Remember that as you insert the distributor, the helical gears will turn the shaft a little, so it can often take a couple of tries before the final position is right. The rotor might also not point exactly where the book says it will. It really is pretty easy to get it wrong by one tooth, so it's worth trying different positions.

Now...I hate even to bring it up, but if the engine was just rebuilt, and the distributor is not at fault, and nobody can find an obvious problem, I think your next step might be to double-check the timing of the camshaft itself.

problem solved

Thank you Mr. Currie Sir,

I went out, cut off one of the retaining tabs on the distibutor. That allowed me to turn the distibutor more (counter clockwise).
It runs smooth throughout the rpm range. Starts easy too. Just needs a little fine tuning. I suppose I should have have mentioned that it now has an aftermarket cam in the first post.

Now on to the next project. 4 1/2 lift and 31' or 32's. havn't decided Rusty's (budget) or RE $$$

Thank you SIR...