Mitsubishi Repair: 1999 Mitsu Galant Burps going 60mph!, bam bam bam, clogged catalytic converter

Question
I have a 1999 Mitsubishi Galant 130k miles. Over the past year,on and off, and only at higher speeds on the freeway, when i let OFF the gas, the car burps and jerks bad(backwards it feels like, and it makes a "bam-bam-bam" noise), and the second i get back on the gas it stops. Seems to be worse when the car is lower on gas and when going down hills, although it does happen w/a full tank of gas and on level ground. It does not do it every day, sometimes it will go a week w/o doing it, then will do it everytime i drive it for days, then stop again. No problems when going at lower speeds or starting/stopping, only on the freeway 60mph or so. What do you think it could be?

Answer
Bridget,
You may have a clogged catalytic converter.  If you've been noticing any smoke, foul smell, or excessive amount of soot from your tailpipe, this can also be a sign of a troublesome catalytic converter.  Poor gas mileage is also an indicator.  

Aside from that, you may want to get a good old fashion tune-up.  Spark plugs, fuel filter, air filter, fuel pump, and even a timing belt replacement could cure your "burps".  But have a mechanic inspect the exhaust system and do a basic tune-up on any of regular maintenance item that's been over 30,000 miles since they were last serviced.  The worst case scenario would be that this is a transmission problem, but I would not expect that to be the case.
Good luck!