With the water heater supply shut off and the circulation pump shut off. All hot water faucets and shower valves get cold water coming through. New water heater installed by Lowe's. Everything work fine before the new water heater. Thermostat is pegged hot and hot showers are pathetic. Installer say it is bleed through? Maybe from a one of the three shower valves?

The newer shower faucets are what is called scald guards.this allows cooler water to temper the hot water. This may be your problem. You mentioned a pump... what kind of pump? Is this a return circulating pump? Did you have a check valve in the cold supply before lowe's came? A check valve is usually on cold line to prevent hot water from rising into the cold line during heating expansion.
Your description would indicate a cross connection between hot/cold lines somewhere. If no problem existed before the new water heater install, I would look there first... were any faucets installed since then? Are their supplies hooked up correctly? Hot on left, cold on right?