I just remodeled two bathrooms (1 and 2) and Bath 1 has a trickle of hot water that is not is barely warm at both the shower and sink. Bath 2 (located 20 feet away from Bath 1) is fine as is the rest of the house.

I installed a single lever Price Fister shower valve (Home Depot) and a Danica single lever faucet attached to existing water lines. I had to reconfigure the copper pipes to change from a two valve shower control to a single control and did solder the new sections behind the shower control valve.

Show us pictures of what you did.