Re: MPG while towing; It depends on the trailer. I have a light utility trailer that tows at the 18-19. Same for my lightest boats. My larger boat, a Viper sailboat, tows at 15 on the highway. I haven't done any long trips with the big camper, but in rush-hour Atlanta traffic, I've seen 12. It seems that the engine doesn't matter much for towing MPG - small engines get the same bad mileage once the trailer gets heavy enough. Even the guy who tows his Viper with a 4-cyl Subaru gets about 15 on the highway. (But he saves when he's not towing)
Re: IRS Section 179; Section 179 is the way that small businesses can purchase capital assets and count them as a current-year expense instead of being forced to carry them forward and claim annual depreciation. It saves tons of hassle and paperwork and allows your paper profit to more closely match your actual cash flow.
So, I drive for work and my truck is owned by my company. The IRS has tons of special rules for claiming vehicles. Basically, you are limited in how much you can expense for a car, but "trucks" get special treatment and qualify for "accelerated depreciation" under Section 179 - meaning they can be fully expensed in the year they are purchased. The definition of "truck" is anything over 6000lbs GVWR. So that's why the GVWR is so important for me. On the 4th gen Runner, the only model with a GVWR over 6000 is the 4wd v8.