Trouble accelerating like its not getting fuel?

The problem:
The car starts fine, no auditory signs of anything being wrong.

whenever you start to move is the problem, when you give it gas the engine starts to react (rpms rise however high, depending on how much gas you give it) but the car has to slowly build up momentum to get moving.

by slowly build up momentum, I mean that it rises at a rate of about 5mph every second; regardless of how much gas you are giving it, or how many rpms the engine is turning.

the rate that the momentum builds up is the same even if you only lightly push the gas, and if you floor it (tho if you floor it, it will do a jump when it switches gears at very high rpms, but speeds are about the same)


ok, first to eliminate suggestions
after the problem started I did all of the following:
1) complete tuneup, new plugs, cords, oil/filter change, air flilter change, radiator fluid, etc.

2) took it to a friend up at nissan service center, they checked for codes, and then checked a few other things (MAF sensor, compression, etc [can't remember them all]) they were stumped, and suggested we check it with a muffler shop for the catalytic converter

3)took it to Pronto Muffler, and they did a full check up on it and said that, there were no codes (which we knew), and that the cat and entire exhaust system looked fine. I had them drive the car, to see if that would help them better understand the problem. And they checked the cat again. They then said the cat is fine and replacing it would probably not fix the problem, and the technician said that it felt like the vehicle was starving for gas when it accelerates.

4) with a lack of option I called firestone and asked what they would charge to look it over and try to find the problem, after explaining the problem, they referred me to AAMCO for the transmission. AAMCO did a full check on the transmission and said it was in good working condition and was not the problem. They did say that the front cat was running way too hot and was probably plugged or clogged, and that I needed to bring it over to pronto muffler to have it checked out (they are within a mile of each other).

5) I took it BACK to pronto and told them what the AAMCO guys said, they checked the car and said that they could not find a problem with it, they would replace it if I wanted to but they ust wanted me to know before hand that it is perfectly fine and would probably not fix the underlying problem.

so now I am just sort of at a loss of what to do.
any suggestions would be greatly appreciated.

-Jeff