ranger running problems (help)

[Jakes01234]

(coworkers truck)
He was driving home last night the truck was running rough.. It felt like it had an exhaust brake..
After forty mins of this it all of a sudden felt back to normal again and everything felt perfectly fine..
He left work to go to school got ten mins down the rode did it again and when he drove back the muffler was cherry red and the paint was all missing ( he has a stupid cherry bomb on it but wasnt red because of that).
Any ideas to what it could be?
Thanks

 

[russrad25]

Plugged cat, misfire (more likely). What year, motor are in it? Have him pull the plugs and see if they are fouled, Could be a coil pack has gone bad, or is on the way out.

 

[Jakes01234]

its a 93 with a 4.0
thanks