Hi Tom and welcome to the forum. Glad to hear from another Ridgeline owner although I do believe you will be looking for another TV in the near future. I tow a much smaller Jay Feather Sport that comes in under 4000# loaded (the rated GVWR is more, but I weighed it at a CAT scale on the way to Disneyworld to get the actual weights). I towed it over 5200 miles last summer and had no problems but I personally wouldn't want to go much heavier than I am. We had to make a panic stop in SC and all went well with my Prodigy brake controller, but it was scary nonetheless.
Here's a link to a post with some photos of my setup,...
My Ridgeline is a 2009 and my understanding is that the gear ratios were changed that year. I average 12 MPG towing and get 22+ MPG when I'm not towing. I do try to keep the speed under 65 when towing and that helps with the gas mileage. There's a lot of information on towing with a Ridgeline over at the Ridgeline Owners Club forums. If you have any specific questions for me just send me a PM and I will get back to you.