We may have played our best BBall already. That said, knowing for at least a month that you are "in" leads to less intensity. No excuse, we should not have lost to GT.
Keep in mind some teams that have already locked their conference titles aren't going to play as hard now and through their conference tournaments. They've been playing for 3+ months and their coach wants them to get fresh legs going into the big dance. It's a good time for the unexpected to win their conference tournaments and get auto-bids.
Roy Williams was famous for resting his players when he was at Kansas. They played, but not as hard as they could.