When getting the donor Envoy XL for my I6 to V8 swap, I towed the Envoy with my SWB 4.2 Envoy about 2-1/2 hours from Columbus to Cleveland. I used roughly a 3,500 lb tandem axle heavy equipment trailer to do so, so easily over 8,000 lb. My Envoy is lifted and has z71 springs in the rear and a 4.11 TBSS rear axle, so it helped with heavy tongue weight and I have a brake controller and trans cooler. Was it advisable, probably not, but it pulled pretty good for a smallish vehicle with a 6 cylinder. I kept it out of OD the entire time and got around 13-14 mpg.