Not really too hard to figure out. You have a 3800# car with a small block, a big open plenum single plane, a set of 3.55 gears, relatively low compression with aluminum heads. The cam hasn't been degreed and who knows what else hasn't been done?

I'd start by degreeing the cam, and then changing the rear gear. As Mr.P mentioned, has a stall test been done on the converter? Putting a little more arm in a small block doesn't turn it into a big block. You may have gotten away with these things with a stroked BB, but not with a small block. I'm sure with a little tuning and changing a few things it will perform like you want it to. Just be patient, it will come around.