Glad it worked out. When you say cooked at 170, do you mean 170°F and via sous vide? Or 170 centigrade/340°F? If the latter, then I’d agree with your thinking that 3 hours was probably too long. Unless you where shooting for fully cooked all the way through, like you might do for pot roast?
I forgot to mention that you can treat sirloin tip as a London Broil if the piece is basically of that method’s standard shape; just marinade and grill or sear. Very thin bias cuts once cooked to med-rare. I’ve made London Broil of pretty much all cuts from the round, except the eye.
I did an eye round Tuesday for sandwiches and had it in a 230°F oven for about 3 hours to get internal 125°F. Then let it rest for about 30 mins while the oven got up to 550F and gave it an 8-minute sear that way. Let it go to RT then chilled it overnight (to slice easier - I have a really cheap slicer and it needs all the help it can get). Then gently reheated a bunch of it for lunch sandwiches yesterday.
