Volumetric efficiency has been improved with new exhaust ports borrowed from the Corvette, while dual catalytic converters and exhaust pipes minimize back-pressure and provide more power. What all this translates into is significantly more power in the standard GM heavy-duty offering with improved fuel economy and even better reliability. To compliment the new engine lineup, GM has two all new units added to it's existing transmission offerings for 2001. First out of the block is the new smooth shifting, German made ZF S6-650. This slick new six-speed manual transmission is the first of its kind in this segment to be offered in both gasoline and diesel powered vehicles.
First gear is designed as a 'creeper gear' for better low-end performance and towing.
With reverse and first gear in the same shift gate, users can throw the gear lever forward for reverse and straight back for first, which should make snowplowing and low speed maneuvers a bit easier. Sixth gear is positioned away from the seating area, giving more room to both driver and passenger during extended highway cruising. This transmission is also equipped with a PTO provision providing up to 25hp capacity. Allison is a leading supplier of automatic transmissions for large application commercial truck and bus markets. Taking those years of experience, they have supplied GM with a great unit full of wonderful features.