Air Flow problems

I have a 1995 Chevy 1500 reg cab short bed with a TBI 350 with hooker supercomps, and true dual exhaust. I dont really count the K&N top mounted Hot Air intake as my import friends like to call it, but that was before i realized that go was ALOT more important than Show. Not too long ago I had my heads ported and polished and had bigger valves cut. Afterwards i noticed that i was bogging pretty bad off the line, but pulling real hard after about 2000rpms. I had a 3.08 rear with an open diff, so i swapped that out for a 3.73 with an Eaton Posi and I am LOVIN IT! I can launch it from almost 2 grand and it hooks fine (as long as the street is clean, Haven't been to the track yet) and pulls like its goin out of style until about 4000 rpms, where it just seems to lose power until it hits 4500 and shifts and get me back down into the good power. I dont spend much time above 4000 but its enough to be annoying. I raced an accord last night, little farty thing and i jumped about a car and a half on her until i hit 4000 and then her acceleration matched mine until my auto shifted at 4500 and i started to pull hard again, and after i get out of first i dont really have the problem anymore. I'm thinking that I might have an airflow problem now... as in not enuf. I came about this theory because since the TBI (that is my problem that TBI crap) anyway that TBI manifold is dual plane (of course) and that means that each time one of those 2.02 inch intake valves open they have to pull 87.5 cu in. of air through a 1 11/16 inch (i believe it is) hole in one side of the throttle body. I may be way off here, but could this be the culprit? And if so is it worth it to get a bigger TBI and have the manifold ported or buy an edelbrock? Or should i ditch the ghetto-jection and cough up $1-2000 for some real MPFI from Edelbrock or do up a nice TPI system.
Thanks,
Chase

well when they did the heads they installed a new cam too, however i know it wasnt real agressive at all, so i wouldnt doubt that, and i thought about the fuel thing today as I was goin to buy my history book, but i confused myself and talked myself outta that theory... i dont really know why. Thank you, ive asked this on 3 different message boards, and i am including all the information i get from other is my other posts... i really appreciate the input.
-Chase Smith

You never mentioned any work done on the fuel injection - fuel pressure changes, chip changes, injector changes, etc.

You have modified the motor to draw more air, and unless you modify the fuel system to flow more fuel, you will have problems (too little fuel fot the air - so too MUCH air, so to speak)

the flat spot at 4500 is an indication that your fuel curve is off.

If you don't understand TBI, you don't want to go farther with TPI, etc. The systems work on the same principles, so you gotta know the basics first - you can't diagnose it unless you know how it works, or is supposed to work THEN you can decide what is NOT working as it should and then you have your FIX.

As soon as i get a chance to go back home the shop that did my heads is gonna burn me a chip using the dyno. I was thinking about what the first guy said and some other things i saw online today and really began to consider the fuel system and such. I began to think there had to be a real significance to it because for example with Edlebrock's MPFI system requires a new fuel pump, and most other systems use an inline pump and then in SportTruck they installed Vortec heads on a truck like mine and recommended the use of a 454 TBI... Thanks very much. I am sure Adam (the chip man at RPM Cylinder heads and machine shop) will be able to help me out here. They've done a chip on a Vette (old TPI) and an eclpise GS-T and got a good bit of horsepower out of those... they have done many more, but those are the only two cars that i know personally.
Thanks Again,
Chase