How do I test individual coil packs on a 2003 F-150, 4.6liter Triton V-8.

I got this truck and was running rough. Previous owner told me the coil packs are going bad on it. I changed the plugs and put the dielectric grease on the spring where connects to coil pack and to pug. No difference. I have not gotten codes pulled yet. Just getting started in the diagnostics on this.