Threaded shower valve connection

I installed, and reinstalled x2 a "Tuscany" branded shower valve today that I couldn't get tightened/ sealed properly. It has only the option of threaded pipe connectors. I used NPT 1/2" brass nipples off of Sharkbite drop-ear elbows/ 1/2" PEX. I tightened the nipples/fittings 1 - 1.5 turns past finger-tight with 2 wraps of regular teflon tape and both supply connections leaked past the threads. I took them apart, cleaned them up, and reinstalled with pipe-thread compound (thickly and uniformly applied). This time 2 leaks rather than 4, but still 1 on each nipple. I took them apart again, cleaned/reapplied/re-tightened and crushed the fittings trying to get them to realign in the proper position (down) to tie into the main supply. Soooo... I replaced the fittings and still 1 leaking thread connection. I don't trust the shower valve body to be threaded properly, however maybe I'm not doing something correct that one of you can point out. I've got 13 years of sub-contract/ contract framing and remodeling experience, but this is my first "major" plumbing/electrical project at my in-laws home. Should I wait for pipe-thread compound to "set" prior to pressurizing the lines? The packaging says it's not needed, but I'm not sure.