How much should I worry going through deep ruts and dragging my differential?

 

??

 

I'm assuming mud but if it's hitting rock and you bounce you can damage the differential. If you haven't high centered the diff you may be ok but you are running a risk of damage any time you do it.

 

Yes through mud, sorry should have been specific.
There's a trail here that leads to a messy mucky incline that's a lot of fun, problem is getting to it, the ruts are deep and muddy I have nice tires and go 1-3 mph through them but I can hear my underside rubbing the whole way

 

Ruts can be deadly in many ways, it depends how deep and what's in them...bolders and logs can do some damge. The oil pans in these trucks can't take much of a hit, - one small bend in the pan can easily cost you engine quickly....the pick-up screen is very close to the bottom.
Max level of submersion is the center of the hub/axle. Sort of bi-law, deeper than that and you should check all your fluids. Actually, ford has that in the owners manual as well if I'm not mistaken. I played in the mud lots when younger.

 

That's a good looking truck, I'd suggest that you suggest filling the ruts a little bit so you clear.

Edit: Either that or you need larger tires.

 

Right, you never know what's going jump out of a rut.