I have a GMC with 6.6ft bed on a double cab. It has the in bed Curt turn over ball hitch (any turn over works fine). I changed the ball to a Curt 4" offset ball and I use the Andersen Ultimate Aluminum (32#) Fifth wheel hitch. Works perfect, no slider needed. My 5er is the 11k weight Wildcat Extralight.
2016 Wildcat 295RSX - 2015 GMC 2500HD DblCab Duramax/Allison 4x4 Z71 6.6' Bed Maxxis 16"E; AirBags;Andersen Ultimate Alum. 5erhitch w/Curt 4" offset;GrndCntrl 3.0 4pt;6000# Dexters;CRE3000 w/Wetbolts; Champ.3100 Invrtr;Furrion48 RearCam;King Dish Tailgater