2000 Safari Coil Problem

I am hoping for some help with my 2000 Safari. In the past 6 months, I have burned out 2 ignition coils. After replacing the coil about 2 months ago (coil #2), I changed out the ignition module at the same time (hoping this might be causing the coil to burn out). I have probably 5,000 mile on the new pieces and can already feel the van misfiring when on the highway between 65-80 mph. Soon it will misfire at all speed ranges and the coil will actually have burn marks through the side. Any ideas what may be causing this? By the way, I also changed out the cap, rotor, plugs, and plug wires.