Larry,
Do a search of the Recipes section, there are three or four threads that specifically discuss fajitas.
When I make fajitas, I usually cook the meat to rare (120-125), let it rest for 10 minutes or so, slice it and then stick the slices back on the grill to get some marks on the individual slices, you need the grill to be really hot at this step to prevent over-cooking the meat while still giving it grill marks. Try squeexing some fresh lime over the meat while it is resting, before putting it back on the grill the 2nd time, gives it a little extra flavor. Usually I will stick the tortillas on at the same time to give them some marks also. Finally, a cast iron pan on the grill works great to cook the peppers and onions. Good luck.
Tim