We just modeled our bathroom with all new tile..tub..and faucets. When we turn on the single handle faucet to about 1/2 to 3/4 on the shower starts to flow pretty good. When the faucet is all the way on...shower stops. Tried new diverter...still same problem. Took off the diverter and had galvanized pipe on...same problem. Guy used pex and sharkbites to attach to new valve. Riser from bottom of tub to shower is 69 inches. Could this be problem? House psi is 95. Would pressure reducer vlave help with this? Local plumber said valve was hooked up wrong...looks good to me and others. What can I do?

Thanks for assistance