It's been a long time since I had the 4 runner, but I know on the rav 4, sometimes you have to put the car in first, jockey it a tad, then shift into reverse. If you're not in the right position, it won't just slip in.

'94 extra-cab 3.0 extra slo (auto tranny) original owner. E/B o/s valve heads and no more crossover. More mods to come.