I am having trouble with my engine in my truck. Its a 88 with a TBI 350. It stumbles like the transmission is stumbling and backfires under heavy acceleration. The backfiring is not very loud, almost like a popping sound in the engine compartment. I took it to a local shop and the mechanic said it was the ignition coil going bad. I replaced it with a new one but it is still acting up. The timing was also checked and it was fine. It seems to be worse when the truck warms up and goes into over drive. The check engine light has not came on. Could the catalytic converter be clogged. Could the fuel filter need to be replaced? When the truck is in park and it is reved up there doesn't seem to be a problem.