If I'm understanding you (Kaman??)...do you mean Kingman, AZ or Kanab, UT? Then you mention Flagstaff?? 89A doesn't run into I-40; 89 does from Bitter Springs to Flagstaff.
So...if you mean from Kanab, Ut and taking 89A from Jacob Lake to Bitter Springs, you'll have a steep downhill just past Jacob Lake but very doable with your equipment - many RVers do it...we did it with our 40' motorhome. Just downshift before you start the descent, don't try to do it once you get going down. It'll be over before you know it! :) Midway down the hill is a very wide scenic overlook on your right; (wide enough for 3 semi trucks parked next to each other) so plan on stopping and taking in the sights.
Continuing on 89A to 89 at Bitter Springs and then south to Flagstaff you could have a few options. On 89 at Cameron, take Hwy 64 west to Grand Canyon Nat'l Park. Your RV would fit in the 3 campgrounds - Desert View and Mather are lovely dry campgrounds; Trailer Village has full hookups. This is your best bet for touring Grand Canyon.
Another option is taking 64 west into Grand Canyon and just park at some of the pull-off for the canyon if you don't want to spend time there. At Grand Canyon Village exit on 64 at Tusayan and 64 south will take you to I-40 at Williams bypassing Flagstaff.
Or you could continue south on 89 and just before Flagstaff to the east of the highway will be the turn off for Sunset Crater Volcano Nat'l Monument. Go on the paved road for a couple miles and just before reaching the ranger booth for the national monument, on the left is Bonito national forest service campground. It's a beautiful place to stay...they don't accept reservations but we've always gotten a site if you arrive early. No hookups; flush toilets.
Then continue into Flagstaff and I-40 west. Have a good trip...beautiful country.