2016 Frontier uses the same Roadmaster kit as our 2009. I remember drilling the frame, not the (so-called) Bumper. I know the thin "high strength" steel used in unit body/frames is a bear to drill, sounds like you got into some of that. It isn't too bad if you have:
1. Powerful LOW-RPM Drill
2. An excellent Drill Bit (No Harbor Fright here!)
3. A Lubricant
I remember drilling the threads out of two large weld nuts in the bumper area and using 1/2" bolts with nuts. Also drilling crosswise through the frame.
Was installing 344-1A. What did you use?
You'll love the truck! Smooth, quiet ride, still a tough little truck. Yours oughta be fast. Our 2.5L 4-cyl, not so much.