I have towed 3 RVs with my 2012 F350 with factory brake controller, a forest river 38' 5th wheel , a 34 heavy TT and now my Landmark, with the 1st two I had the controller set to 5 and everything stopped fine now with my Landmark I have it set at 10 (highest setting) and it slows the RV down but not a lot, is this normal for Heartland?