2000 Jeep Cherokee laredo

Having an occastional hesitation type problem upon acceleration and when this happens there is a smell that comes from the driver front wheel well. Onnly this side, not the passengers. The chek engine light never comes on. I checked the transmission fluid and it looks and smells okay with a red tint. Note that the Jeep has only did this a couple of times and usually after about 10 minutes of driving. Then if it is parked for any lenght of time, usually will not do it again on the same day. Any suggestion will be greatly appreciated as my freshman college son drives this vehilce from New Orleans to Baton Rouge which is about 70 miles one way. I just don't want him having any major problem on the highway. Note, my mechanic replaced my front rotors and brake pads about 2 weeks before this intermittent problems began. Until that break job, we never had this problem. Lastly of interest, when this problem is occurring, if he puts the car in park, then shifts either into drive or reverse the car does not move at all, just like if the car was braked. But if he gives it gas the car will move, but again as soon as he take his foot off of the gas pedal it will roll to a stop. Now when the car is not having this intermiiten problem and you go from park to reverse or drive it of course begins to roll at a good clip like most cars do. Thoughts?