It isn't the BB per se that's the problem but the entire GXP system i.e. crank and BB. In order to be different from Shimano and possibly to skirt a patent, SRAM designed the crank spindle with a reduction at the left end. Shimano spindle is 24mm throughout. A tube's diameter is very important to stiffness and larger is almost always better, even if you use less material.
The GXP system is a 24mm spindle that reduces to 21mm or 19mm on the left side (I can't remember the exact dimensions). In other words, the relatively untaxed right hand bearing has a 24mm spindle through it and the highly taxed left bearing only a 21 (19?)mm spindle through it. The amount of flex at this joint puts the bearing out of alignment with hard pedal strokes. A deep groove ball bearing can't run out of alignment without premature failure.
A crank spindle only transmits torque from the left crank. The right crank takes up force directly from the crank into the spider without any torque going through the spindle. All BBs have this problem but some are better designed to cope with it than others.
GXP thus has a double weakness - the thin spindle is weaker than a thick one and the thin end is at the wrong end, hence premature bearing failure. GXP brags with "technologies" such as gutter seals - whatever that is, but it is all in vain. They may as well have had no seals considering how short-lived the left bearing is.
So
@Jenkins, if you want to solve the problem, the only way is to get a Shimano crank, I'm afraid. No fancy brand name BB can solve an inherently poor system.
