Absitively - if the piston doesn't fully retract, the drain ports do
not fully open.  The brakes on one end will work fine when cold, but
when they heat up the fluid expands and has no place to go.

 Third or fourth hard stop, they get hot, the fluid expands, and one
end's brakes won't release, no matter what you do.

 Don't ask me what the slop spec is, but there is one - probably one
or two MM.   I figure if the piston is fully retracted to the stop
c-clip or pin, the pedal doesn't have a weak return spring and it's
fully retracted to it's stop, and there's noticeable wiggle room for
the pushrod, you should be fine.

 If you're getting oddness like that., you may be by elapsed time
alone better off to go through and change out the master cylinder,
calipers and wheel cylinders, and rubber brake hoses - just on general
principles of 18 to 19 years of the rubber parts' exposure to ozone
and contaminants.  Rebuilt parts are cheaper than a nasty collision.

 I did it to my Corvair after several years of it sitting, and I'm
told there were a few surprises found when he did a post-mortem on the
brake parts.  And with a Pre-1966-ish car with a single braking system
any one failure knocks out the entire brake system.  It's due again
after another sitting parked for several years period.

 Your truck has split brakes, but a front brake failure will still
get exciting if it happens at a bad time, as the front brakes do most
of the heavy work.  The rears only will get you stopped - eventually.
If you don't have the time or room for the extra distance...

   --<< Bruce >>--