Here's another couple of thoughts:

Are you wearing the right shoes? Have you changed anything- do they need to be replaced etc?

I wouldn't overthink the pace of the long slow distance run. If your previous runs were at a reasonably easy pace for you- stick with that and do what feels natural. I run a lot on hilly dirt roads and the pace doesn't eqate at all with pavement. For me, while there's a time to pace myself (eg tempo type runs), most of the mileage I do is at whatever speed feels natural (with occassional violent jerks into the woods when the dog picks up a particular scent, but I don't recommend that).