You can tow to ratings. Personally I would not go over #8000 gross. That is just me, for no reason, other than me being a belt and suspender type guy!
That engine "screaming" up hills is doing just what it is designed to do. Hemi makes its power at I think around 3600 rpm,(screaming). If you don't want to listen to an engine running well within its design parameters, sell your truck and buy a diesel!
I have a '13 Ram and it gets my juices flowing when tugging up a hill in third gear, the thing just pullin like a freight train!