the allison is using ALL 6 forward gears for towing....no problems at all....70mph in 6th gear is around 1700/1800 rpm depending on tire size. when towing and climbing hills adding throttle to maintain speed; most of the time you will be able to stay in 6th gear depending on the speed you want and how heavy the load is; if for some reason you cannot maintain speed and continue to ad throttle the trans will down shift to 5th gear raising rpm to about 2100 allowing you to climb the hill easier. very nice to have such a small gear change not like going from 5th to 4th which is a big jump in rpm.....only once did I ever have the trans go into 4th on a hill and then i just backed off and moped along at 55mph to the top...
suspension wise the 01 thru 10 models are all the same...it is the HP/TQ rating of the engine that changed over the years allowing you to tow more with the added power...
the new 11 model has new suspension and frame parts for more in bed truck carrying weight and new HP/TQ numbers for even greater towing
2007 Chevy Classic Ext. Cab Long Box 4x4 LBZ; 5" Magnaflow turbo back Exhaust; Firestone Ride-Rite Air Bags; Tow Mirrors, EFILive for all other needs
2012 Chevy Cruze Eco 1.4L Turbo 6sp