The highest ranked team TU MBB has ever defeated is probably a somewhat forgotten game in the early moments of the 1996-97 season. The preseason NIT had TU at #5 UCLA. On the website, here's a link to a Classic Moment:
http://www.tulsahurricane.com/watch/?Archive=3372
http://www.tulsahurricane.com/watch/?Archive=3372