97 Monte hesitating

Have a great 97 Monte with 202,000 recently starting to hesitate slightly at 52 plus or minus MPH. It's a wierd feeling like the tires aren't in contact with the road for a nanosecond. All other gears shift smoothly, response is instantanous otherwise. Stepping down creates quick response. Some chatter at lower speeds sounds more like exhaust issue than transmission. Seems like this issue started with new tires about 6,000 miles ago and is more noticeable on wet roads. HELP! Suggestions? Don't want to give up my other-wise perfect car!