The easy way to tell if they are good:
With the shock off the truck, compressit fully and release. The piston should rise very slowly, and at a steady rate to full extension.
If it doesn't rise at all, the shock is dead, worthless.
If it rises, but changes rate as it rises, the shock has a wear spot in its bore, and is also worthless.
I'd be VERY suprised if they are still good with that many miles because our short wheelbase is tough on shocks. I've had to replace mine almost every year.
John C.