Try moving the trailer with the 7 pin plug UNPLUGGED from the tow vehicle. If it moves fine, it is not the tow vehicle and something else.
The problem with most items can be determined thru the process of eliminiation.
2012 Fun Finder XT 276 Toy Hauler & Harley Davidson Ultra Classic with Condor wheel chock
2014 Dodge Ram 2500 AT 4X4 Crew Cab 6.4 L Hemi, 373 gears, tow package, Rambox option, Revolver X2 tonneau cover, Equal-I-zer anti-sway hitch.