More than likely the transmission torque converter is going in and out of lock-up. There will be nothing wrong with the trans itself. This issue is from RFI electrical noise interference caused by the alternator being picked up by the TPS circuit going to the PCM. There are several ways to fix this issue. The aftermarket offers a in-line noise suppressor to stop the problem. Me being a cheap a$$, have found another way to remedy ths issue at almost no cost. The first thing you need to do is remove and scrub down your battery cables and post VERY well. This can be half the problem all in itself. After you do this, find the large alternator ground wire goung from the alternator to the passenger side battery box. It will be black w/ an orange tracer. Go into the kitchen and steal a couple of pieces of aluminum foil and wrap this wire several times around from the bottom of the tray to the alternator. This will help shield some of the electrical "noise" from the alternator to the PCM. I have fixed many of them this way without a problem. Give it a shot. You may be surprised.