Try adjusting your brake controller so that there is a little more on the trailer brakes. A good friend of mine bought his 1st 5er last year and had the same problem with his Reese slider. He went back to the installer and they adjusted his brakes and that seemed to correct the problem.
Vinnie and Chris
2013 2WD Chevy Silverado LTZ 3500HD Crew Cab Short Bed Duramax/Allison Reese R16 Slider
2014 Crossroads Cruiser Patriot CF305SK