first gear slippage

Any ideas on why my son's 2001 Grand Am does not go into first gear smoothly when taking off from a stop? A mechanic said the motor mounts were broke----this turned out to not be true. (He wanted to charge $600 plus to fix 3 motor mounts that were NOT broke!) Another mechanic can not find where the problem is. He reset computer codes, did some other non related work (replaced gasket, intake manifold, fixed some broken wires). He took the car for a drive, and it did not jerk in first gear. After a little more work (minor---broken glove box), and drove it again---The car was again not shifting into first right. The car has 86,000 miles on it. Now the mechanic thinks a filter may be plugged. The transmission oil has not ever been changed in the car. The car has been driven hard---long commute to work, through alot of traffic.

Does anyone have an idea what is going on here? You comments are much appreciated.

well, personally, 86,000miles + not having changed the transmission fluid, just might be the transmission going.

I would try a transmission fluid exchange (where they pump new through it with a machine) I have heard one other time one doing this and they rebuilt the tranny. Could also be a bad shift solonoid.

Thank you for your replies.
The transmission was serviced, and we picked up the car. Now it is shifting roughly into first gear, AND overdrive.
Before the car was taken to a mechanic, there was a hard thump when coming to a stop in reverse. It did that for a day, then stopped. Hasn't done it since.
I find it strange that after the mechanic reset computer codes he took it for a test drive, and then said it was no longer shifting roughly. Then it started doing it again after replacing gasket, intake manifold, and servicing the transmission.
The service engine light is on (has been). The mechanic had said he fixed that---was a broken wire. Evidently not the case. (He had to go out of town when I picked the car up, so I didn't get a chance to talk to him. Will do so today.)
Wish the car was paid for so my son could get rid of it.
Thanks!

Have you tried going to a Pontiac Dealership yet to have them look at it? When I was having problems with my trans, they told me there was an update for the computer, that would stop the "gear slippage" that i was encountering. That may be the case for your car.... especially since the mechanic claims that the car runs fine after clearing any codes. Unfortunetly for my car the update was not the issue, but my Catalytic Converter was clogged causing all my problems. Maybe this will help you out a little.

Ya i was having trouble with that in my 1996 Grand Am. I would put the petal to the floor and will accelerate at a slow rate and the rpm's would stay at 2500. When usely I put it to the floor I would be set back in my seat. So I called my friend who is transmision guy, he told me to check my fuses in my car. So I took off my fuse panel pushed in some loose fuses. I pulled my car out of the drive way, put the petal to the floor and I leave a 15+ skid mark.

Ya i was having that problem in my 96 Grand Am