My daughter has an 04 Grand Am with the V6, trans works very smooth until car has been running 15-20 miles, time for everything to get up to running temperature. Car will be doing fine driving down the road, then come to a stop and when trying to accelerate it has problem with going. It seems that a brake is holding but then as speed slowly increases it will jerk a couple times then when speed comes up above about 30-35 it seems to get back to running OK. Then if stopped again it does the same problem all over. It sort of seems to be "between gears" . Car runs great until FULLY Hot. Any thoughts?