If you take 89, coming out of Page near the jct of 89A you will have a 5-mile section of 6% downhill with a runaway truck ramp which exits to the right.
Taking 89A coming from Jacob Lake you'll have 10 miles of 5-6% downhill with 35 mph curves and switchbacks and long drop-offs.
We've done both multiple times with our 40' motorhome. Get into low gear before you begin descents; not in the midst of one.
By now in your trip you should be a pro!
Even if you just drive up toward Jacob Lake you can then do a flat drive the Grand Canyon North Rim for a looksee. Then retrace your drive to get back to Hwy 89 to Page if that's the one you want to do. You will also be close to viewing the South Rim on your way to Flagstaff. Take Hwy 64 west off 89 - a easy drive.