Your stock 4runner should be fine but I would at least recommend some better than OEM tires on it for the trip. I was on alpine loop a couple weeks ago and it seems rockier than last year. I would also recommend black bear pass if you are going to be in the area but do that in the middle of the week. Both black bear and Imogene pass get super crowded on the weekends. The whole alpine loop takes more like 6-8 hours but if it's crowded like it was when we were there and someone in your group has vehicle issues, then it's at least 12 hours. There's a pretty good bbq place in Lake city called Southern Vittles. Take plenty of water and be sure to drink it even when driving up there. I would also recommend you spend a night somewhere on the way up there that's about 7k in elevation to help acclimate your body to the elevation.