KV-1 and KV-1S: 15
M3 Light: 6
The Sherman, despite having similar dimensions to the T-34, can only sit half as many men. That is because there are no surfaces above the tracks to stand on, and not nearly as many handles to hold on to.
Of course, official numbers didn't stop creative arrangement of larger number of infantry. Here you see 8 soldiers riding on a T-70 instead of the "official" 6:
The manual also has some data for trucks:
GAZ-AA 1.5 ton truck ("polutorka"): 10-12
ZiS-5 truck: 16-20
ZiS-6 truck: 16-20