Well, I posted a reply from home, but for whatever reason, it's not
Was the truck doing this before you had it tuned up? Was the tune up
scheduled maintenance or were you trying to correct a problem?
If it's an '88, it should have TBI (throttle body injection) instead of
a carb, although at first glance (and to the inexperienced eye) the TBI
unit looks a lot like a carb.
If it's TBI, it should have an O2 sensor. When the engine is cold, the
ECM (computer) runs the engine rich until the O2 sensor heats up to
operating temperature so that the oxygen content of the exhaust can be
properly measured. If it's disconnected, damaged, or just plain bad,
it could be causing the ECM to believe that the engine isn't fully
warmed up, and therefore keep the mixture too rich. Could be the ECM
Hopefully someone with more experience can chime in to answer this more
in depth than I.
Does it smoke a lot when you start it? How about when you drive it?