In my mind, it's not about the gas tank or the end of the road. We now employ a system that forces turnovers and relies on relatively strong shooting / guard play. If a team handles our pressure relatively well, they tend to shoot very high percentages because much of their offense is fast break oriented. If opponents handle reasonably well and we shoot poorly, we are going to get it handed to us. Some nights the ball just doesn't bounce right for pressure defenses and we have little to fall back on during those stretches.
Other teams that have employed Pearl's style of play (a la Nolan Richardson's Arkansas teams) and found ways to win even without turnovers from their opponents had (1) Deep benches and could wear you down over time with tempo (2) The ability to defend well in the halfcourt (3) the ability to score in the paint from a set offense if need be to take defensive pressure off of their shooters (4) Strong rebounding to start the break and put back misses to set up the press. Of these listed, we might have (1), but the remainder we lack because of post player issues. While I think we've gotten better in the post, on both ends of the floor, I don't think we're going to beat competitive teams when our pressure fails to generate turnovers and up tempo play.