What do you intend to use the truck for? Will it be your new plow rig, a back up truck, or a straight up swap for your current (presumably functional) truck? Even if the engine is bullet proof, you're still talking a truck that is 20 years old. Is it a manual or a automatic? Keep in mind the additional expenses that an additional truck will bring, registration, insurance, upkeep.
I'd offer 4k then try and flip it for a few bucks if you have the time and desire to do so.