I have a 2006 Chevy Tahoe z71 with the towing package. I have seen a 2007 Gore Thoroughbred two horse with side ramp that I really like. 7'9" wide aprox 17' long. 3420 lbs empty 2660 hooked up hitch weight 760.

I have a Warmblood and sometime may haul for a friend. I am from Va. and we do have to travel over a few hills and one some what intimating mtn.

Should I down scale and keep looking? 

This might help ya out a little.

http://www.rvtowingtips.com/horsepower.htm

no one can answer that question but you.  but bear in mind from a 17 foot 3500# to say a 12 foot 2800# is not going to make much difference imo.  the tahoe will handle the load easily, with the exception of the tongue weight getting out of hand (the tahoe max is 1000# w/WDH iirc).  i dont know if gore would be any help with an estimate loaded tongue or not.  i pulled the 2h slant in my sig for a couple years with my trailblazer, much smaller and less powerfull than the tahoe, the trailer empty weight was the same as the gore, however the empty tongue was 650# and loaded to go was ~1000#. i wasnt going to win any races, but it was a solid and reliable performer....actually exceding my expectations and delaying the purchase of the diesel in my sig...which btw fell short of my expectations.  i guess it depends on what youre expecting.

whatever trailer you chose may i suggest, as a wdh will likely be  necessary on your tahoe, taking the time to learn about wdh and how to properly set up/use them? you can not rely only on the dealer/installer for such "complicated" adjustments.

good luck.

SEE SEE I was good and didn't say s..t about not enough truck,or bigger brakes,or nuthin.