Heres some pics of My 96 crew cab dually taking my 1972 C50 stake truck to the scrap yard with a GVCW of 26,500 lbs I towed it 60 miles. The stake truck weighted 10,500 and the trailer is about 7,000.
With my new Westers reflash ECM she towed it great on a 91 deg day with the air on, EGT's didnt get hotter than 800, trans temp was 200, and coolant got to 220 once going up a big hill.
Not to bad for a 11 year old 6.5
-96 6.5TD K3500 Crew Cab Dually 4x4, 97 cooling mods, Dmax fan, 3.5" downpipe, 4.5" straight exhaust, intercooler, custom intake plenum, fast idle switch, Ranch Hand bumpers, Turbo Master, egt, boost, & trans gauges, 6" Superlift, K&N off the turbo.
-88 6.2 3/4 burban 255K
-83 6.2 CC C30 220K
-82 6.2 1/2 4x4 burban 270K