EAT MORE COW MEAT
Much better grilled over very low direct heat with the lid shut.
If you have a charcoal grill that allows you to drop the coals lower in the grill or raise the cooking grate real high above the coals, that's the way to go.
Basically, what you're cooking is a long thick steak. It won't take over an hour to cook, and tenderloin is very unforgiving if you overcook it. It has a low internal fat content, and will become dry and livery if overcooked. We pull ours @ 115* and rest with a foil tent.
Something else that will help is to remove the side meat. There is a pretty tough membrane between it and the main body of the tenderloin that ought to come off. Also, be sure to remove all the silverskin for the best dining. You'll cut a fair amount of meat off when you remove the side meat, but it's good saved over for kabobs.
Rub with EVOO or melted butter before grilling or the outside will tend to be pretty dry. I've cooked a few dozen of these, and they're super good if you do them right. If you don't, you're better off cutting them into steaks.
Oh, and one last thing, tuck the tail under itself and tie it in place or skewer it. That way the whole length of the meat will be uniform ad cook evenly.
Oink snort Yeah, you did say BEEF tenderloin didn't you?