My Mom always used to use some generic meat marinade mixed with wishbone Italian Dressing. I didn't remember which random packet she used so I decided to try the McCormick Grill Mates Montreal Steak seasoning we use on pretty much everything (burgers, steaks, pork chops). I've marinated with it before just a few hours on NY strips and it was good. This time I put the top round in with the marinade on Thursday afternoon so it marinated about 48 hours :) its smelling pretty amazing on the grill.
3lbs top round steak
1/2 cup olive oil
4 Tbsp balsamic vinegar
4 heaping tsp McCormick Montreal steak seasoning
At least 1 tsp of minced garlic, I put 2 in because we like garlic.
Poke a bunch of holes in steak (both sides) with a fork and put in a gallon sized resealable baggie. Mix marinade and pour in, press air out and then seal. Swish around to mix seasonings up. Put meat in the fridge and turn it at least twice a day to evenly marinade.
As far as the broiling or grilling goes, you'd best find a recipe but we always use two burners on the gas grill. Heat both burners to high then turn off one and put the meat over that. Switch every 20 minutes or so and don't flip the meat for at least an hour. Low heat & slow cooking along with the long marinating time makes the meat nice and tender.
Then we slice it thin and use the leftovers for french dips (just use a packet of au jus) the next day :) Or make hot steak sandwiches.