Preheat your grill to 345°F.
Brush the potatoes with some of the melted butter, season them with salt and pepper, then place them over the “on” side of the grill on the warming rack to bake.
Prepare the beef by scoring the fat cap in a diamond pattern, then rubbing it thoroughly with the steak rub.
Combine the red wine and beef broth in a measuring cup.
In a small dish, mix 6 tbsp. of the beef broth mixture and 2 tbsp. of the melted butter. Suck it up with your marinade injector. In several places over the roast, insert the needle of the injector and depress the plunger as you pull the needle out slowly. Do this at least once with a full syringe. If it is a large roast, you can do it twice.
Place the roast into a roasting pan with a lid, (make sure that it fits on your grill) and place it over indirect heat to roast.
Roast the beef for 35 to 50 minutes, or until a meat thermometer reads medium rare, about 145°F.
When the roast is done to your liking, remove it from the grill and place it on a plate to rest, covered with some foil and a tea towel. While the meat is resting, check the potatoes. Fill the marinade injector with the remaining butter, with garlic powder added and inject the potatoes in several places with butter. Turn off the grill but leave the potatoes until you are ready to serve.
Make the gravy by pouring any of the meat drippings into a sauce pan over medium-low heat. Slowly add the flour until you have a thick paste. Whisk in the remaining red wine and beef broth, a little at a time, until you have the perfect gravy consistency. Remember you will need more or less of both the flour and the beef broth mixture for doing this.
Slice the beef, and serve it with the potatoes, topped with your favourites like sour cream, chives and bacon bits, and some veggies too. Don’t forget the gravy.