Like Foot Stomper said, if it's solid, it's solid. If it's not failed, peeling, cracked, sanding it and applying a coat of primer over it to start your new paint job is how most paint jobs start.
There is something I don't see mentioned here on this subject and something I usually mention right off the gitgo when this subject of stripping comes up.
That would be that if you do strip it,
DO NOT STRIP MORE THAN YOU CAN HANDLE IN A DAY! Strip a panel or two and get those into primer, then move onto the next.
DO NOT STRIP THE WHOLE THING AT ONCE!
This is a
HUGE mistake and one I have seen many times over the years.
There are few things more overwhelming than a complete bare metal car or truck sitting in a garage, whew, that is hard to take even for a pro.
You could even do the worse panels that you know need to be stripped or close to it, strip them, get them in epoxy primer. You may find out after doing those that the rest of the truck is just fine!
Brian