1999 Pontiac Grand AM transmission problems

While driving at highway speed, transmission lost gears upper gears. After towing it in, dealer said that gears 3 and 4 were completely gone. Explained that sometimes leakage occurs from inadequate seal from factory, causing this problem. Another grand am owner also had this problem, only at 37,000 miles, just out of warranty.

I have owned this car for 3 years after buying it used.it had 32,000 miles on it and ran well. Now for the last year the transmission has continued to give me problems and is getting worse.I have had it serviced, computer diagnosed twice and had it serviced again. All of this has been out of pocket and cost me down time of use of my vehicle.it shifts hard (randomly) , has hard vibration at idle, acts as if it wants to stall and is slow going into reverse.