I think Mack first got that label when he coached at North Carolina and could not beat FSU. I did not understand that. FSU was loaded with talent back then. Mack built a good team, but I never expected them to beat FSU.
Brown then takes over for Texas. That is a different situation. It is easier to get talent at Texas than it is at UNC. During his time, he has lost some very high profile games. Any OU game and the Big 12 championships to Colorado and Nebraska. I would say Texas had the same amount of talent as OU, if not more in a game or two during those losses. They were easily more talented than CU. Those losses are on him. He was very tight during those games. He didn't let his players play. He let Vincy play last night and it made a difference.
For example, when Texas lost the close game to OU in 2001, freshman Cedric Benson did not play a single snap. Even as a freshman, he was the best back on the team. He could have made a difference. In 2003 against Arkansas, freshman Vince Young never saw the field. He was an overly cautious coach that tended to try not to lose games. I don't see Bob Stoops keeping his talented players on the sidelines.
I do give credit to Mack leading Texas to victories at Nebraska. Those were big wins and came at a place that is usually very tough to win. But I think they really weren't big games. In 1998, Texas was an underdog and given no chance to win. With no chance, comes no pressure. He seems to coach differently in those situations. The next time they went to Lincoln, Nebraska was just not a good team.
Mack broke the choker label when he won a close game in last year's Rose Bowl. It seemed to change him and the way he coaches and that was reflected this season with the big win at Ohio St., beating OU, the Big 12 and now this. He may need to win a few more to guarantee the label is dropped, but he is on the righ track.