My 2 cents....
1. It difficult to flood out the engine of a UTV. Buddy is right, just needs to stay running. I don't think letting off the gas is an issue as long as it still runs.
2. With the weight you are describing I'm assuming your looking at a crew. I would look at a dual axel trailer. Not only will it trailer better, you will get better tire wear if you tow long distances. I don't like to push the upper limits of the trailer, especially if you want to put other gear on the trailer with the UTV.
3. If you don't mind the drive and are looking Polaris, try Hoffpauir in Goldthwaite.
Hope that helps