88 Tempo Poor Performance

88 Tempo, 62k miles. Tuned up, all filters changed new oil, flushed coolant system, fuel additive used, replaced serpentine and alternater belts. Tested alternater, it is good.

Car was a grandma's, very nice, started and ran smooth for first 200 miles I owned.

Vehicle ran poorly one evening so I parked it in the barn, would not start next day. Ended up starting with either. Not a cold day.

Check engine and amp light appears while attempting start but go off once engine is started. Engine operates well in park and nuetral, once in gear, engine hesitates and acceleration is extremely slow. Engine acts like it wants to "flood out" at 45 to 50 miles per hour. I replace the ignition coil. No change.

Friend suggested catalytic converter may be clogged from sitting a long time. I drilled a quarter inch hole at converter. No help.

Please assist! Thanks!