Terrible acceleration to 3000rpms then takes off like a scalded dog???

[Knuckles69]

Wonder if someone can point out what I'm missing here. Bought this 98 altima 2.4l automatic about a month ago and i've been trying to get the gremlin out of it since. Here's my problem: When I pull off from a green light I have terrible acceleration (whether Im lightly touching the gas OR foot to the floor), but once I hit 3000rpm the car takes off. Runs perfectly up until it shifts. The second I drop below 3000(after shift) im immediately back to that terrible acceleration until i reach 3000 again. Car idles fine in park but idle drops when I shift to drive/reverse. (not sure about neutral, i will check tonight). No check engine light on.

So far I have: replaced spark plugs(OE NGK coppers/double checked gap), replaced cap & rotor, replaced fuel filter, ran a tank of seafoam through it (skipped a tank) then a tank of Lucas fuel injector cleaner, all injectors are clicking normally, replaced air filter, cleaner MAF sensor (CRC MAF cleaner), repaired post-cat exhaust leak, and nothing has had any effect on this problem what-so-ever

Anyone have any ideas?
I've added a bottle or Lucas transmission fix to the trans: shifts smoother, but had zero affect on the acceleration issue, which leads me to lean away from the torque converter.
I've pulled the vacuum hose off the fuel pressure regulator to see if fuel came out. (it didnt) so i assume thats good. (is there another way to test it?)
Used 2 bottles of carb cleaner spraying around the intake manifold to check for leaks and other misc hoses. Not sucking air anywhere. And I Sharpied my coolant level on reservoir (on the chance that the intake manifold was leaking coolant). has not dropped in 500miles
Checked that O-ring on the distributor that always leaks; not leaking
Barely touching the accelerator or mashing it foot to the floor has the same results under 3000 rpm, so im doubting TPS
Car uses a timing chain instead of belt so I doubt thats been changed to throw the timing off. I'm stumped. Thought these new cars where supposed to throw a damn check engine light when something went wrong?

Car has 215000 miles on it and a grand total of $850 in it (purchase price+ parts) so id like to avoid the $250 diagnostic fee if possible. Ive put 500 miles on it since I got it and it is 100% consistent at 3000rpm, every single time.

All thoughts, ideas, and half assed guesses are welcome! thanks guys.