Son's Grand Prix

Son has 1994 Grand Prix with 3.1. About 120,00 mi. Problems with trany started about year ago and he never did anything with it. First started on being able to take off in D (step on gas and it slipped like it wasn't even in gear), get going in 3rd and then shift up. Later he had to start out in 2nd and then shift up. Once you got going you were fine until you stopped, then same process. It did get so when you took off it almost hammered or clunked into gear.
This fall I had transmission flush and change and next son drove it to college. Also put in Sea Foam transmission fluid. Be darned if it didn't work perfectly for about week. Then for a while it would only slip when you first started out and then be fine. Now several months later we are back to starting out in 2nd. Son is getting different car so in one respect no big deal with this one, but body is in real good condition and motor is sound and they will only give me $400 for trade in so I'm just going to keep driving it to work being i have 30 miles of open prairie. Any ideas on possible inexpensive fix or should I just drive until it doesn't go anymore? Appreciate any ideas. Thank you. Hope I did this right!!

I moved your post from the tips and maintenance subforum to the regular forum for better visibility.

Your problem is likely sticky/bad shift solenoids or internnal valve body issues. If Troy1 sees this (he's our trans expert), he'll be able to help you better.

Appreciate your moving it. First time trying this forum thing and had a heck of a time just getting it posted to start with plus the fact I'm not much of a motor head either. Hopefully I'll find some good info that won't be too spendy to try.

Does anybody have any suggestions?

If you had the trans flushed, and by flushed I dont mean going to one of those quick lube places where they stick a hose down the trans and suck the old fluid out. What I mean by flushed is having the pan removed, fluid drained, the valve body cleaned, new filter and pan gasket. If after that, the trans misbehaves, then the 1-2 band is worn and you will have no choice but to tear-down the trans or have it replaced.

Did have the complete flush and filter change. Actually I believe they flushed the whole system with more transmission fluid then just draining and replacing. Appreciate the comments and guess I'll just drive it until it doesn't go anymore.