Pencil it out first, pretty easy with some solid assumptions (miles per year, commuting distance, fuel/ins/repairs, ownership cost and salvage value etc for each option. 1. Diesel and beater car x 6 years. 2. Newer 1/2 ton, no beater car x 6 years. 3. Diesel, no beater car x 6 years.
I've done this before and typically (unless you can be Suuuper saavy with the beater and fix it yourself, get a great deal and don't mind driving a sardine can to get 35mpg) one vehicle, even racking up miles on it wins over 2 vehicles.
Of course there's other things to consider, especially living in the rust belt. Does the expensive truck stay parked and the beater gets the salt season duty? Otherwise, that's a valid cost, in that your truck (either one since both in your scenario will be 10-15 years old at the end of the term, both being expensive and retaining value better than a beater with a heater) will likely be or be on it's way to being a rust bucket.
Once you do all the numbers, then let your emotion and inner skin flint decide if you want to continue driving that 1998 Civic around or if you've earned the right to travel in style!