1. Year and engine version (we should be able to figure out version off year anyway)
2. Transmission (manual or auto)
3. Any and all modifications done to the truck
4. 2wd or 4x4
5. Gauges installed? No more than factory gauges?
6. What are you doing when problem occurred? Any sounds with symptoms? Or symptoms with sounds?
7. Specific rpm, or speed associated with symptom/sound?
8. Only happens when cold/hot, loading the engine/ no load (idle or cruising down hwy)

All this info allows us to be as close as we can to test driving your truck via the interwebz. Be as specific as you can please. It not only helps give us an idea of what could be the problem, but it also helps you by us being able to rule out a few possibilities just by conditions.