i own a grand prix and have not had any problems with the tranny yet,
but...i also own a grand marquis and even though it's of course not a
pontiac,and i'm not sure how close gm trannys are to fords,i had the same
symptoms as yours with my grand marquis,the car would work fine in
reverse,but you had to gun the hell out of it in drive to even get it to
move ahead very slowly,after several seconds of high rev,.it would start to
inch ahead very slowly,but move.  it wound up being the a defective trans
strator and the defective part fried the forward clutch plates,i did the
rebuilding in my garage with the help of the internet and a few mechanics
advice,but it was very time consuming and hard even though it cost a
fraction of the price to do it myself.