I was going to buy an Eco with max tow and hd payload but couldn't find any with both for under $40k. For whatever reason they were together only on the higher trim levels. To me the hd payload is a must because it gets you the heavier rear end with 7 lug wheels.
I ended up talking my way up to a three quarter ton. I could technically squeeze by with the half ton but I live among big mountains and wanted a little more margin for safety. Plus the exhaust brakes you can get on diesels stock these days are awesome.
I guess I'd just give a look at some of the heavier options out there. Stepping up now is cheaper than going half ton and then trading in three years from now.