BB help, please!
1) Can the Truvativ GXP BB be used with Shimano cranks or can it only be used with Truvativ cranks?
2) Is the Truvativ GXP BB better than the Hope BB with the "BB Truvativ GXP Conversion" kit?
I can't speak for #1, but the consensus is that the stock bearings in the entry-level GXP are rubbish. They definitely don't turn as nicely as others that I have used.
Check out these upgrade kits. There's nothing wrong with the cups for the bearings, just the bearings themselves.
No for #1, GXP and HollowtechII are different specs, and incompatible.
I always upgrade my bearings to enduros, 5 minute job if you have the tool.