"Serv 4WD" light activated only when towing

I have a 2015 2500 Laramie Crew Cab Short Box. The "Serv 4WD" indicator light comes on when I tow my 9,000# travel trailer, and only during towing. Myself nor dealer can get light to come on during any other conditions. Without fail, the light will come on one once highway speed (65-70) has been achieved after 5-10 minutes of towing. Stays on until vehicle is shut off. No particular conditions exist (uphill, downhill, wet, dry, cold, hot) when light activated. Performance of truck is not affected either. Truck is in tow/haul mode with exhaust brake activated whenever I tow. Truck currently has 88K miles on it. Dealer is servicing under warranty. Service Mgr just informed me he received some new info from Ram and wants truck back next Mon to attempt another fix. This will be their 3rd attempt. This has happened 6x since April of this year. Can anyone shed some light on this? Chris in Lakeville, MA.

 

Stored fault codes???

 

My code reader has not indicated any stored fault codes, nor has dealer indicated any. As a matter of fact, I was required to tow camper on way to Ram dealership in order to activate fault so tech had something to go on.