Yes, yes, not a 6 ton.
Yes, they are still in wide spread use.
Yes, there is a newer variant kicking around. Follow the link in my signature block to see the A3 variant. The one I have is the M36A3 which is the extended wheel base variant. The A3 variant is not is wide spread use.
The M35 series is currently being replaced by the Family of Medium Tactical Vehicles (FMTV) made by Stewart & Stevenson in Texas. It is replacing both the M35 series and M939 series trucks with a 2½ ton and 5 ton FMTV variant.
The only difference between the 2½ ton and 5 ton FMTVs are the 5 tons have a third axle and the "deuce" version only two axles. Again, if you follow the link in my signature block you will see both a 2½ ton cargo, 5 ton cargo FMTVs as well as a 5 ton FMTV wrecker. A lot of folks are mistaking them for West German MAN made vehicles.