A truck is for hauling heavy and large things. While it's true our obesity rate is on the rise, you would be better off with a fuel efficient people mover. The problem with a truck is it gets half as many mpg as a compact, so you are bleeding money right there. Also, I don't believe most trucks qualify for Uber. They don't accept all makes and models and cars can't be too old. I know they don't accept two doors, for instance.
I was very happy with my Chrysler Town and Country and I am very happy with my Kia Soul. However, my soul gets double the mpg as the minivan but the minivan allowed me to do uberXL trips, so they kind of weigh each other out. I think I prefer the Soul because of maneuverability. It is fun to drive smaller cars that you can see very well out of. I do lots of U-turns and lane changing.
I know people with a Prius get 60+ mpg so that is very helpful for earning money.
But my BIGGEST recommendation, and this goes for anyone not just Uber drivers, is to get a car that costs under $8000 that you can pay in cash or pay off quickly. It will depreciate way slower than a more expensive car. And depreciation is a huge expense. My 8000 Kia has only depreciated to 5000 in 50,000 miles! So a cost of .06/mile.
You can calculate depreciation estimate by going to cars.com and looking for a car, and the same car 3 years older with 50,000 more miles and see how much less it is worth.