I just bought a 1996 hijet deckvan, and it runs very good, for the most part. under normal driving conditions you would never know there was a problem, but if you "punch" the throttle, the engine bogs down. I'm not sure if this started after I bought it or if it was doing it when I bought it because ive never had any reason to punch it. yesterday I got into a little mud and when I hit the gas pretty hard, instead of going, it bogged down. what might my issue be?