I had a 2010 Ram 3500 DRW, crew cab long bed 4X4 with 68RFE and also a 2012 in same configuration..both with 4:10...Towing sig 5er weighing around 16,100 to 16,300# and I put the truck in tow/haul with EB on and never de-selected a gear....I just towed and let the truck downshift if and when it needed it...I do all my towing in the mountains and never had an issue. the 68RFE seems to be a much maligned transmission, but I never had a problem...Again, guess it would depend on your gearing, but with 4:10, it was rare, if ever that I "towed in 4th or 5th", if that's what you meant...I let the truck gear down when it needed to and it worked great...and I came from a Chevy D/A combo:).....
