I've been keeping an eye out for a 15-18k gvwr truck for a while. Been looking mostly at f450-550's but was wondering if anyone had any of isuzu/mitsubishi style trucks. What do you think about them?
Advantages/disadvantages?
I bought this 2004 Isuzu NPR stakebed (8 x 14 ft) last Dec. $11K off eBay.
49,500 miles on the odometer, 6.0L (360 cid) V8 (LQ4) Chevy engine. 12,000 lb GVWR, 18,000 lb GCWR. Weighs about 7100 lb with me, my tools and 3/4 tank of gas. Runs great--75 mph unloaded on the freeway. About 12 mpg unloaded-- 9-10 mpg with a load (my tractors are in the 3000-3500 lb range)

Use 10 ft aluminum ramps (5000 lb rating) to load my parade tractors. You need to place a couple of jacks under the rear end to keep the truck level when loading.
Assembled a lightweight rear fence so I don't have to wrestle with those
heavy steel fence sections
Installed an 8000 lb remotely controlled Warn winch
The NPR diesels are also nice, have higher GVWR (15000-18000 lb), but run $4-5K higher in cost than the 6.0L gas engine. The tilt cab makes engine servicing/repair pretty easy since there's no fenders in the way to limit accessibilty. The front axle is pretty low to the ground so it's not that easy to work under the truck in that area without ramps--no big deal.
Most NPRs are rigged as box trucks--stakebeds are a lot rarer and ones with a Supreme bed like mine are even more rare. Of course, you can always upfit a NPR box truck to stakebed configuration.
Good luck.