A 1500 Suburban or Expedition EL will tow a 5000 lbs GVWR trailer fairly easily especially without a big family onboard. The small V-8s with six speed trans (in the GM< not sure about Ford) is pretty efficient for a large vehicle.
However, this isn't what you want to buy for an 8000 lb trailer...if you are buying new, you only real choice for that is the 2500 Suburban, which they say is NOT available for the 2014 model year, unsure if it is gone for good or just on hiatus.
If it doesn't have to be a 4WD SUV, a full size van is also an option, particularly the Ford with the V-10.
