2000 Ford F-150 Coil on plug?

I had #8 coil on plug go out. I replaced it with a new one myself (I however didnt use dielectric grease) right after changing it, it ran great but I picked up an intermittant flutter/spark knock while accelerating. It only started after I replaced the coil. You can cut truck off and back on and it quits fluttering. Could me not using the grease be causing this problem, like I said it started soon as I changed the coil. Thanks in advance for any answer! ---Sean