Installed new Moen Positemp, center of back wall 15" off of tub....... spout left wall up 6" 28" from valve............. shower head 55" up. Not getting water from spout when opening valve, getting it at shower full pressure. Driving me nuts!

Does you spout have a small knob like this one? Moen 2353 Chateau Posi-Temp® Single Handle Tub/Shower Chrome - Faucet Depot (http://www.faucetdepot.com/prod/Moen-2353-Chateau-Posi-Temp®-Single-Handle-Tub-Shower-Chrome-4073.asp)

Have you removed the spout? If so, and still no water, remove the cartridge and blow through the spout pipe with spout removed. If you can't blow through it, the valve body or piping to the spout is clogged, most likely with solder. You may have to unsweat the spout drop pipe from the vavle body to investigate further. Please let us know what you find.