1993 Dodge Daytona Misfire

My boyfriend's 1993 Dodge Daytona with a 3.0l engine is and has been having a very bad misfire since we met. She lack power coming off the line at a red light and when he tries to accelerate passed about 45 MPH she'll sputter and seem like she wants to stall in the middle of the road. He's changed fixed the exhaust valve guide power that tends to happen with them, pulled the injectors and still cannot seem to find out what the problem is with the car.
The only reason I'm posting this question is because we have a bet to see who can fix it sooner. I think it has to do with the exhaust leak that he can't seem to fix but he insists its something in the engine compartment. Could we both be right or wrong? We both going to an automotive training college, so you'd think that we would know what the heck is going on, but sadly, we don't.
Any help will be awesome. Thanks a bunch
Rebekah Lynne