1996 Pontiac Sunfire Died will not start

My car was originally a 2.4L engine. It was changed over to the 2.2L, using the motor, trans, complete engine wiring harness and computer from a 97 sunfire that had 50,000 miles on it. (That was a little over 100,000 miles ago.) My car recently started dieing at highway speeds after driving about an hour. It would coast about 50 feet and start going again. I put a used fuel pump assembly and a new fuel filter on it but it didn't help. I then put a new fuel pump assembly on it and it ran good for 3 days then started the same thing again. After a couple more days it started cutting out while driving, died and wouldn't start. No fuel and no spark. (It is not giving any computer codes saying there is a problem.) I have replaced the fuel pump assembly again, key switch, computer, wiring harness under the hood, all fuses, all relays, crankshaft sensor, coil pack, reset theft system and it still has no spark and no fuel. Any suggestions on what to try next would be appreciated. (The engine cranks over good, dash lights are all on like normal when the key is on, I have power in and out of all the fuses in the fuse box, checked with test light.)