Neither of the recent military variants of the 737NG have any mods to the pressurization system as mentioned above, and they are very likely to be staying aloft for some very long flight times, quite regularly!
It's 8400 feet for most of the trips, the auxiliary fuel system depends on that cabin pressure, as it's regulated from the standard NG differential.
And for the same reason, you won't see any one of them dumping fuel below around FL200 either!
Cheers....
