02 shifting problems
 

hello everyone, I have a 2002 Monte Carlo that i have owned for about 3 years now. I just had issues with both the motor and transmission so i had both replaced within a month of each other. Once the car came back from the shop i noticed that the car would stall kinda when increasing speed. I was told BY THE SHOP i needed to replace my fuel filter. OK i did that and two days later the car just stopped shifting. it wouldn't drive, reverse or anything. I assumed it was the transmission once again (yes i am in the process of getting my $1200 back from this shop) After allowing the car to sit a few days my husband went out and tried to drive it and it shifts fine for a while and then nothing but when we turn it off for a minute, it goes back to shifting fine for a while. Its like something in the car has to be reset or something. I know nothing about cars and neither does my husband and we don't even know where to begin to fix the problem. I have been told everything from we need bolts on the torque converter to the transmission needs to be replaced again. I just wanted you guys input on what you think it could be. Thanks for any response