On all my vehicles when towing a heavy trailer close to the limit I installed an extra separate transmission cooler and never pulled in overdrive mode. Dont forget that your 3000 lbs dry weight is probably close to 4000 lbs + with the propane. Battery, all the goods you bring in the trailer plus the occupants and the rest. Towing in mountainous regions in really taking a heavy tool on the powertrain.
Traverse 2017, chevy Uplander 2009 LT short wheelbase, Impala 2003, jeep cherokee Laredo 1990, chevy citation 1984 2.8 v6, vauxhall Firenza1972, rambler american 1964 model 330, vauxhall velox 1956 rebuilt, NSU Prinz 1961 2 cylinder micro car rebuilt, Renault Dauphine 1960 rebuilt, ford prefect 1952 ( english car with non hydrolic brakes rebuilt. Honda 1986 motorcycle in new condition and 13 travel trailers from a Boler 1300 to a Rockwood mini lite 20 feet.