89 south out of Jackson you'll have Salt River Pass which is 7% grade for 3.5 miles - south of Afton. Easy drive - you won't even notice it. Further south on 89 you'll have Geneva Pass between Geneva and Montpelier, ID. You'll have 6% for 2 miles. I'd then suggest taking 30 to Kemmerer then 189 to I-80 at Evanston, WY.
At Evanston head west on I-80 to Heber City on Hwy 40. Jordanelle State Park is very nice with big sites. Then pick up UT6 to Helper, Price and Green River,UT at I-70. Go east on I-70 a short distance to Hwy 191 and on to Moab and on to 163 to Monument Valley at the Arizona border.
If you want to go to the Grand Canyon continue south o 163 to Kayenta, AZ then west on 160 toward Tuba City, AZ and Hwy 89. Take AZ89 south a short distance to 64 west which will take you into Grand Canyon NP. Leaving Grand Canyon take 64 south to I-40 at Williams, AZ.
I would not recommend 191 in Utah (Flaming Gorge area). Coming down to Vernal you'll have approx. 10 miles of 8 & 9% grades with switchbacks.
I would also recommend that you purchase the 'Mountain Directory for Truckers & RVers' before you go then you can read up on roads and you won't get any surprises.
It's understandably difficult for flat-landers to get into the mountains the first time. However, when you're finished with this trip you'll be a pro. For the most part you'll get a gradual introductory once you get out of the Plains. Even heading to Yellowstone if you stay on interstates you'll still have some 6% grades and even steeper on I-70 west of Denver if you take that route. Don't be afraid of some of the secondary roads. That's where you find the beauty. Have a great trip!
