Slice whole picanha WITH the grain using two fingers as thickness guide, about 2 inches thick; Trim excess fat cap if desired or if necessary.
Season steaks generously with beef rub on all sides (~3 tbsp for 4 steaks).
Set grill to indirect cooking with 1-2 burners on and steaks in the cool (off) zone at 250F.
Cook steaks in indirect zone until internal temperature reaches 115-120F for rare/medium-rare (this took ~40 minutes @ 250F indirect).OR whatever your goal is for internal temperature (like medium), just subtract 10F and take off the grill at THAT temp. So say medium, take off at 130F. Remove steaks and rest for 7 minutes once at 10F under target.
Brush all sides with melted unsalted butter (~2-3 tbsp for 4 steaks).
Sear over direct heat or sear station or skillet, flipping every 20-30 seconds for 2-3 minutes per side until browned.
Rest for 5-7 minutes.
Slice against the grain and serve.