nathos

I bought a bf2 zf xr6t today with 95000km The cars tranny seems fine except under wot the car will rev to red line and sit there refusing to change. To get it to change, it needs to be backed off the accelarator or manually changed. The gears change fine on hard throttle although it won't change on full throttle. I'm starting to get worried and think I bought a dud. I've done a search and can't find anything Could anyone tell me how deep I'm in? Do I need a rebuild? Or is this a common problem with an easy fix?