Milk.
I don't know all the chemistry/details (enzymes I think), but it works.
Trim the meat up nice and clean, put it in a bowl and add enough milk to just enough cover it; put it in the fridge or on the counter depending on meat temp. You want the meat warmed up some from fridge temps when it hits the grill. I use 2% milk because that is what we have in the house. Tenderizing-wise it does fine. Fat content does not seem to matter. (Buttermilk seems to tweak the flavor nicely, and I use it for variety sometimes.)
Try 30-45 minutes on a batch of pieces, cook one piece, and try it. Adjust as needed.
Jaccard is definitely a useful tool, but I've never needed it on backstrap.
+1 on the recommendation to not overcook it, and don't let it cool off either. I sometimes use plates like you used to see in steakhouses, steel inserts in plastic carriers, just to keep it hot. If you are trying multilple dishes at once, pick all accompaniments so they stall well or just plan on a multi-course meal. Get the meat while it is HOT!
Enjoy the fruits of your labor.
