Surging and Stalling. Somebody help!!!!!

[Rodney]

I have an 89 LX 5.0. I replaced the engine with a 5.0 with the following mods: Cobra upper and lower intake, 75 mm Pro-M (clibrated for the injectors), 65mm t.b., 24 lb injectors, 1.7 roller rockers, ported stock heads, E303 cam, pulleys, equal length headers, hi-flow h-pipe(with cats), and flows. When I replaced the eng. I also replaced sa many sensors as I could including the O2 sensors and the pcv valve.
When I'm driving the car and I put my foot on the clutch to slow down, the idle will shoot up to about 25oo rpm and just hang there. At other times it'll try it's darndest to just shut off, forcing me to rev it to keep it running. The smells coming from the exhaust are all wrong, sometimes super rich, other times lean. I've had someone tell me that the stock computer can't keep up with the air and fuel requirements of this new engine, overcompensating sometimes and backing off too much sometimes. That would seem valid if the car hadn't been doing the same thing when it was stock. I was thinking that maybe the stock computer is bad, but I replaced it with another stock computer and no difference.

Any help would be greatly appreciated. This problem is killin me.