I have a 2005 Durango with a 5.7 liter Hemi. I am having misfire issues on number 6 and 3 cylinders.

I have done the following with no success.
1. Spark plugs have been changed.
2. Spark plug wires are brand new.
3. replaced the coil pack.

Still misfires. Does anyone know what the hell is going on here? When it does not misfire, it runs smooth, no issue. Once up to speed there is no misfire and gas mileage is fine.

Please help.