It depends on YOUR situation...
if you've got enough truck and engine, the tranny won't have to be geared down in a lower gear to deliver the power needed....
everyone I know, including myself, does not use tow haul -
unless their tranny is doing a lot of hunting up and down for the right gear...
7000-8000 lbs is probably on the low end of your trucks tow ratings and you probably won't even know it's back there - good choice
While I don't know what a 2005 chevy version of tow haul is, the older fords just basically locked out high gear...
so you were running around in one gear less than you could use and getting poorer mpg - MUCH poorer !
The newer trucks have much improved trannies and engines that are not nearly as taxed unless you get up into the 15 - 17k range even WITH the tall gearing they can put in them ...
Heck, towing my 'horse of a trailer', I even put on the cruise, place it in manual 6th gear and let the turbo work it over anything less than a 3% grade so it DOESN'T go through the downshift, speed up, then upshift, then apply the brakes because it over accelerated the set speed
good luck and once you do pull yours you'll find out ! Now go camping !