A missfire.

This afternoon I installed a new set of Autolite AP 65 apark plugs in my 1983 Dodge van. Since last wednesday when I was pulling a U Haul trailer with my 1948 Jeep on the trailer, my van was making a noise as though it was under a heavy load (Jeep weighs one ton) and some black smoke was coming out of the tail pipe. When I got home and unloaded my Jeep and returned the trailer to U Haul there wasen't any more smoke coming from the tail Pipe and now it still doesn't smoke from the tail pipe, there might be a little bit of smoke when I had the engine running about an hour ago, but it is hard for me to see with my old eyes in the bright sunshine outside. However, when I started up my van a little while ago and with the dog house/engine hood removed and with the engine running I hear a PUP... PUP... PUP... noise. The spark plug wires look to me as though they might be the original spark plug wires. A few years ago when I was installing new spark plugs the end of the rubber boot over the clip that clips onto a spark plug, that rubber portion tore off, about an ince and a quarter long portion. I didn't see any arching as though that spark plug wire might be grounding out on something. I suppose I should buy a new set of spark plug wires. Any suggestions on what I should do? Thanks.