1999 Dodge Ram misfire and oil loss

I purchased a 1999 dodge 2500 and when I got it it had minor tranny problems I fixed them and it ran great for about 2 months then it began to misfire and smoke on heavy acceleration its misfiring on cylinder 8 I replaced the plugs, coil wire, plug wires, distributor cap and rotor, and an o2 sensor. It Burns about 4 qts of 10 w 40 a week. Before it began to misfire the coil wire split and I replaced it not long after it began to misfire. I believe it could be an o ring or valve stem seals but am unsure and don't know how much this should cost to repair or If it is easy to do myself