Don't worry about the grade, we travel that about three times per summer with our FW and boat in tow and it's not that bad, especially if you have engine braking. If you do decide to take this route, make sure you stop at the overlook viewing area just before you turn the corner to Togwotee Mountain Lodge. The view of the Tetons is spectacular and shouldn't be missed. As far as traffic, don't worry about it, you are there to enjoy the Parks, not speed through them so you can go home and tell your friends you visited them. Have a great trip.