On my 06 F150 with 20k miles, all 4 of my BFG's have cracks around the shoulders. The tread is still good, the ride has not deteriorated, but my question: is this an indication of impending failure?

I'm about to take a 1600 mile round trip drive next weekend. Any idea if these tires are warning me that they are going to go out in a bad way?

I have just enough time to get tires from a local tire shop, but not enough time to mail order to save some cash. Local good-year quoted me just under $1400 for everything. I want the silent armor and I like the 275/70/18. Its an E range tire and 33 inches tall. I have the money to get tires, but I really don't need to spend $1400 right before going out of town.

Thoughts if the tires are warning me to replace them?