I just purchased a 92 sedan deville. The car is in very good condition. The engine has a little miss, but still runs very good. The problem I am having is when you put the car in drive and start off, it really bogs down. After it gets going it runs real smooth. If you slow down and then give it gas, it takes off. Just starting from a stop is when I have this problem. Also going down the road, if you floor it, the car does not downshift. I have tried from different speeds. I changed the tranny fluid and filter, still the same. Could this be a vacuum modulator problem, or a motor problem? Thanks ahead of time, I am new to this site, but not new to working on cars.

Not exactly sure but it sounds transmission related. Either that or it could be the catalytic converter, I've heard of that causing some bogging issues, but it doesn't quite fit the question of why it doesn't downshift while moving.

Well, I tried the vacum modulator, but that didn't help. It was cheap that is why I tried it first. I guess I will take it to a shop and let them hook it up and tell me what it needs. I was thinking about the converter also, that is my next thing to try.