You've done two things wrong.
1) You did not Gap your plugs... consult your owners manual for correct gap.
2) You used Platinum Plugs... Many Dodge vehicles do not respond well to Platinum plugs.
Get Copper Plugs Gap them correctly, remove the platinum garbage and install your copper plugs. Don't forget some dielectric grease on the wire connection part of the plug, and some anti-seize on the threads.
If the problem comes back then swap the coil from the misfiring cylinder with another "good" coil from another cylinder, if the problem stays at the original cylinder then you know you have a bigger problem, if it carries to the new cylinder then you have a bad coil.
Let us know how you make out.
Oh and Gapping Tools are like $5 at the autoparts store, so no excuse not to have one.