That has always been a problem- teams can have long sustained drives against us and we have a VERY hard time getting off the field sometimes. It was true against Baylor and Oregon as well.
If I'm an offensive coordinator looking to come up with a game plan against BYU's defense I'm looking to use my quarterback to run read options and the running back running downhill to get 3 yards at a time. Those long drives can wear down an defense.