Pontiac Problems? Ask a Mechanic for Answers ASAP
At this point I would not start at the dealer. There is no doubt that the problem is internal.
My recommendation is to have the transmission flushed before you take the next step. The next step unfortunately is having the transmission disassemblied to find the source.
I can tell you that I have had excellent success flushing transmissions with these types of problems. The flush is a 3 step process that involves adding a cleaner to the fluid, I then drive the cars for about 10 miles to allow the cleaner to work completely through the valve body and clutches.
Next, the flush equipment is connected and ALL of the old fluid is replaced by new. After the flush, a conditioner is added..
I can't tell you how many transmissions I have saved with this process....
Please let me know if I can answer anything else for you...
Did you have it flushed already or just a new transmission filter and refill?
I bet that they did only drain the pan and change the filter. Back in the day this was an acceptable repair because there was nothing better. This only removes about 5 quarts of a 14 quart system.
These days the flushing process is so refined that it does often cure problems. You will need to make a few calls to your local shop and ask them if they are able to ...Flush Transmissions...
Getting it flushed is the way to go. If you continue to have problems after the flush then you know what will have to be done...