i just purchased a 2007 1/2 GMC duramax with an allison transmission,with the allision trammy you dont have to worry about going down hills and getting your brakes hot the allision trammy can since the degree of incline and downshift on its on. ijust took a trip to TM factory ,going up 6 degree mountains maintained a 60 mph and tacked 1700rpm and no reb in engine. going down the same hills coming back the trammy downshifted on its on and held the truck at 60mph. i was pulling a 2007 3326 loaded.i had a 05 chevy 5.3 engine and the getting up and down hills wasnt good.hot brakes are no fun.by the way i get over 20 mpg without trailer and 17.8 mpg inthe mountains pulling the 3326 king.i wouldnt trade my truck for two new gas trucks.its nice to come from a dead stop to 60mph in 7 seconds.the towing is 13000lbs. trailer and 16000lbs.5th wheel.check the cost of each and make up your mind. good luck with you decision.
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