We have a 2004 Tundra double cab. I am not sure what the engine size is. It is rated for 6800 pounds. We didn't have much problem with the motor taking care of it. We had a lot of problems with the wind. Any crosswind over 10 MPH would push me all over the road at highway speeds. Couldn't go over 50 MPH once the wind picked up. Part of this could be the way the WDH was set up, but we are over the tow rating either way.
I think I am going to go with the 1 ton. It is a small amount to pay for the added comfort in knowing that there won't be any white knuckle driving this summer.
Thanks everyone for your input. Happy Friday!