2005 Cadillac CTS Transmission drops to 1st before stopping

05' CTS, at times, will feel like it is dropping down to a lower gear too quickly prior to coming to a stop. It almost feels like the brakes are locking shut or we are being rear ended. If you put the car in neutral when coming to a stop, the jolt does not occur. We had the transmission fluid and filter changed, and it was fine for 100 miles then the problem began again. The car sat for a week and the battery ended up running low and we had to boost it. After that, we have gone another 100 miles and the problem has not re appeared. Could this be a computer issue?