durango transmission locks up

1998 Dodge Durango, runs fine when cold, but when it warms up, the tranmission will lock up going down the road(scary to say the least). Anyone have any ideas on this? I hate to think I have to buy a new transmisson.

additional info: no codes with the OBD II scan tool

Never heard of this problem before, when you say locks up do you mean the tranny doesn't pull anymore or actually locks up the tires?! Wow! Hate to say transmission time but....Had any trouble before this? Has it been serviced regularly? The tranny is computer controlled but do you think the computer can lock the trans up?

it locks the wheels up, it was slipping before and I changed the fluid and filter and it ran fine for about two weeks.

Have you made absolutely sure it is the tranny and not a differential or brake problem? If indeed it is the transmission it could be the planetary gear or something similar and that wouldn't set a code but that would be odd.