1996 Mazda B2300 Bucking/Lurching...

I have a 1996 Mazda B2300 SE FWD 2.3L 5 Speed manual transmission pickup. All of a sudden it started running horribly. It idles fine, but when you push on the accelerator, the RPM's immediately drop to below 500 and it will not pick back up until you let off the accelerator. I can baby it (barely push in the accelerator) until it gets up to speed, but then almost as soon as I shift into the next gear, the bucking/Lurching, low RPM's start again. Rarely can I make it to highway speeds, and going up hills is next to impossible. I have replaced the Mass Air Flow Sensor, the computer, and the Crank Position Indicator. (It should be noted that when I replaced the computer I put a computer from a '95 Mazda and it ran a little rough, but the Bucking/Lurching, low RPM problem was not present, but as soon as I put the NEW computer in, it went back to the Bucking/Lurching, low RPM's). I thought since it went back to the problem after I put in the new computer, maybe I got a bad computer.... Not unheard of, so I took the new computer back and got another new computer. No help.

I really need help properly diagnosing and repairing this problem. Any help or comments would be GREATLY appreciated!

Thanks in advance for any help given,

J. Brown