Thanks for the report, the most important think you had fun with your family, were safe and comfortably on the road. Screw the gas mileage :) It's meaningless when years from now your kids will remember camping with you because soon they'll be too big and won't go with you :)
Your 2500 Suburban is the same class GMT800 as your dad's 1500HD, both have very similar chassis with 8600 GVW rating, both have almost same trannies: yours is I believe 4L85E, and his is 4L80E but otherwise almost same trucks. The 8.1 makes a HUGE difference as you noticed.