Grand Teton & Yellowstone Questions

From Cincinnati, my recommendation would be to take I74 to Davenport/Moline to pick up I80 all the way to Rawlins, WY then route 287 through Lander to route 26 over the Togowtee Pass into Grand Teton. Between DuBois and the top of the pass is a gradual climb and the descent isn't bad either. Use lower gears to control speed going down to save your brakes. I90 is much further north and would be a better return route when starting from Yellowstone, which also makes the trip a nice loop.

Excellent route suggestion, with the caveat to make sure to gas up in Rawlins, even if you still have most of a tank when you're going through there. (Rawlins also has a couple of half-decent CGs if you need a place to overnight.) Togwotee Pass is a beautiful ride and not all that hard to tow over due to the gradual grades. For a class C it should be a piece of cake. The Dubois KOA (east of the pass) is a nice overnight as well.

x2 on renting the car at the Jackson airport. Shouldn't be a problem getting in & out of there. DO reserve a car ahead of time. I also second the advice about bikes - don't bother. IMO riding through Yellowstone is potentially more dangerous than it's worth, and the park is too big to see the sights without a motorized vehicle.

As I recall, our phone service (Verizon) was ok at Fishing Bridge last Labor Day, but cell towers in the Lake/Fishing Bridge area are very new.