Leaf - The drive shaft does work in and out of the rear of the tranny as the load changes on the rear axle. That's normal. As for how much slop is acceptable, I don't know. But, I do know that lots of Fords have quite a bit of slop and keep on going.

The headlights aren't on fuses. They are on thermal circuit breakers that trip and then reset when they cool. The high beams on the truck I sold did what you described and I never did find the problem. Always thought it was a short somewhere, but could not find it. So, I'm wondering if the breakers get old and no longer carry enough current for the lights.