My 2000 F350 has the 7.3 diesel, 4x4, auto, high teens to 20 highway mpg but 15 in town, a huge crew cab and can haul a cord of wood with the sideboards on. Even the short bed is 7 feet long. Cost me 10900$ with 127000 miles two years ago. I daily drive it 8 miles each way which really is a bit short for a diesel.
I could not justify buying a commuter with my 16 mile daily commute. The cost of insurance, purchase, tabs, upkeep, etc. does NOT pay for the additional mpg. Not even close. I worry people don't do the math and assume that an additional small commuter car is a money saver.
I do think that you can have a single vehicle meet your criteria. Your arbitrary 20mpg is a touch too high for most trucks, lower that to 18 and you can buy a modern 1500 series chevy pickup and commute in comfort or a diesel truck and really haul a lot with a touch less comfort. That 2 mpg (20-18) won't amount to anything when you do the math.