well a buddy brought his moms car to me - he said it would run fine until you get to around 30 mph, then if you would give it gas, it wouldn't go any where - like the tranny would go into neutral or something the engine would rev up but you couldn't feel the tranny pulling. When i test drove it - it was fine.

Any Ideas?

It would help to post the year Century and which autotransaxle.

it's a 95 w/ auto trans, not sure what tranny is in it tho.

It should be a 4T60E autotransaxle. When was the last tranny service. ATF and screen filter?

And what is the current mileage?

No idea, I doubt if it's ever been done, I test drove the vehicle twice today I took it out and drove around for about 305 minutes and I didn't have any problems with it. I will get the mileage and post it later

let him test drive w/ you in the passenger seat and confirm his
"observations"

The first day I drove it he was with me and he said it wasn't doing it. and it has almost 117k on it