Bill and Elaine,
I think you could do ever thing you wanted in 3 days and that maybe a little too long. It kind of depends on how much hiking you want to do in the park.
I Have never spent more than 2 days in the TRNP at a time. But I,ve never done a lot of hiking in the park. We have done a couple of the short nature trail loop hikes and done all the loop auto tours both in the south and north units. The most interesting loop hike area for us was the coal vein trail, but the fire went out back in the late 70's, so we haven't done that one sence then. Also part of the road in the north unit is closed, but the campground and hiking trails are still open. But some of the trailheads in the western area of the park won't be accessable by road. The road in the north unit isn't a loop drive like in the south unit. Also the campgrounds in the park do not have showers. The RV park in Medora is very nice. Make a reservation for one of the site by the river. Go to the Medora Musical, it's fun and entertaining. We've seen the one that was running last season and enjoyed it. Not sure how many seasons that ones been running, but awhile anyway.
Hey!
If I was you're tour director, what I would have you do is.
Spend 2 days in TRNP, camping Cottonwood CG in the Park, enjoying the nightly Ranges talk.
Next day depart 8:00 AM , or earlyier,taking MT 200 off of I 94 at Glendive and go to Great Falls. You should be able to make the 410 miles in less than 9 hours. On the way through town watch for the Carl's Jr on your right. Pick up a couple of 6$ Burger combo meals, you'll be tired and not feeling like cooking. Proceed to Dick's, after check in, throw your wash in the laundry and while that's working go hit the showers. Remember that $10 a night TRNP CG had no shower.
Next day spend the morning at the Russell Museum and the afternoon at the Lewis and Clark Trail Intrepretive Center.
Next day make another early start and go to GNP. Get on I 15 north take the Vaugh exit, US 89 north. You should be able to make it even as far as Many Glacier's CG by noon. 3 1/2 hour trip with no stops. Less to the closer ones. St Mary and Rising Sun CG's
I think you can have wonderful time and see and do most of what you'll want in 5 days in Glacier.