While I've not pulled a 5th wheel camper in those areas, I have pulled a 53' Semi trailer all over New England with no problems. Who ever told you that might 1) have been inexperienced, 2) traveled every back county road, 3) never drove in the mountains before. If you stay on the interstates, National highways, and State Routes you'll not have any problems. Relax and enjoy some beautiful country side.
2012 Winnebago "Journey To Insanity" 40U
2008 Dakota Sport 4x4
2004 Subaru Baja - DW's
2006 Honda Shadow Aero - TOAD for now.