Rough idle once engine is hot

[forstr]

Truck idles very rough when it gets hot. Did a tune up and noticed that the NO. 8 plug is fouled real bad...still runs the same. Here's what I'm thinking, maybe someone can offer some tips.

 

1. Timing off (affecting fuel mixture)

2. Vacuum leak affecting manifold pressure/injector

3. Valves out of adjustment

4. Bad rings/valves

5. Bad coil (although it only affects one cylinder?)

6. Bad O2 sensor? Probably not...just throwing it out there

 

Please help ASAP!