Yes, Tahoes could get either JB5 or JB6 brakes. Suburbans got JB6 standard which makes sense given the weight.
According to this link here, you COULD get 225/75/R16s, although I've never seen one in my own experience.
Most 400s are 245/75/R16. Z71 and 265s are separate RPO codes. Z71 is the...