From what I understand, the B2 piston and band are required for all forward gears, and needs to be locked when driving to prevent wearing of the friction material.

If it's sluggish but eventually locks the band, you can drive it. If it slips while driving, you won't get very far, as the friction material will be wearing. It's hard to tell if it is slipping while driving since there is always some "slip" in the torque converter.