I had, what I thought was a transmission problem with a 1998 GMC Box Van. I also noticed that the sound coming out of the muffler was not right. It turned out that the problem was a blocked catalytic converter. When replaced, it regained the power it once had. You may also have to replace the filter in your transmission, a service I was told should be done every 50K miles. One other thing, a tranny service by a reputable, (AAMCO), serviceman in your area. I found AAMCO to be good and not too expensive. Hope this helps. Jendo
