Just to throw another possibility into the pile, my 92, 350, TBI w/ shorty headers, a TB spacer and the Edelbrock TBI cam was like this. It kinda crept up on me that it wouldn't rev to save its life. Also has the Flowmaster one in / two out exhaust. It would struggle to get to 4k RPM or so. Went through a lot of diag steps and finally checked exhaust back pressure. Holy cow. Nearly 20 psi in front of the factory converter at 3500 RPM when I stopped the test.
Replaced the converter with straight pipe and viola! Sounded better immediately when I started it. Took it for a ride and it was like I added 100 hp AND it would rev to 5k no sweat.
So, my suggestion is to check your exhaust back pressure on both sides of the converter and the muffler.