Gas Mileage for a 5.3 towing 4500lbs

I just recently got a 2001 Suburban with 76,000 miles on it.  I bought it mainly to pull our travel trailer that is about 3700lbs empty and 4500lbs fully loaded.  I am curious what I can expect in terms of gas mileage while pulling on the highway....any ideas??

Those weights are just for the trailer don't forget to add the weight of the passengers and the stuff inside the vehicle also to reflect the true gross weight. The conditions of towing such as winds ,hills etc. and how the vehicle is geared will affect the mileage as well... my guess ...you might be looking at anywhere from 6 - 9 m/g. 

But the figure of 4500 lbs is with the other stuff and the family.........you still think only 6 - 9 mpg pulling a trailer at that weight?

I'm just recalling the highway mileage gotten with my 2000 Express 2500 ( 350 ) ... the best was 16.5 mpg ... with 1500lbs of cargo.

So you may get a little better than 9 mpg towing a trailer of 4500 lbs + with the 5.3l ... I'd be very surprised if you got anywhere close to 14.

Your gear ratio will also have an effect on the mileage, especially towing.