In a GMT800 he could opt for a 2500 chassis with a 6.0. Maybe even a Quadrasteer! A 2WD Tahoe or Yukon equipped with a 5.3 and a 3.23 gear can tow a maximum of 7,700 pounds with a GCWR of 13,000 pounds. A 2WD Yukon XL or Suburban with a 3.42 gear can tow up to 7,400 pounds with a GCWR of 13,000 pounds. A 4.10 gear and that changes to 8,400 and 14,000.
A 2WD 2500 with Quadrasteer and a 6.0 motor can tow up to 9,700 pounds and has a GCWR of 16,000 pounds with a 4.10 gear. A 2WD 2500 with the 8100 motor (454) and a 4.10 gear can pull 12,000 pounds and has a GCWR of 19,000 pounds.
Download the 2005 GMC Yukon owner's manual and check out pages 4-65/66.
Welcome aboard Duane!