Is a 1992 chevy k3500 a good truck or a lemon

We don't know the condition of the truck but it is 25 years old! How many miles, what kind of maintenance?

Just the fact that you think people online can guess about a 25 year old truck makes me think that you won't know how to go about checking it out for value. So don't buy it.

It can be either... since as was stated and the fact you ask this thquestion with such little information, its clear you can't determine this yourself, do yourself a HUGE favor and pay a mechanic to thoroughly go over it. Might cost $100 or so dollars, And the advice they give you would be worth every penny.