The hot water side of the tub faucet runs slow, the cold water side runs fine.
I've changed the manifold and installed ball valve shut offs.
The water still runs slow. All the pipes from the water heater are copper.
Thanks

Is that single handle tub faucet ? Do you happen to know its model / brand name ?

Newer type faucets have anti-scold device built in that could be adjusted - or they also may have pressure balancing mechanism that may not be working properly.

Faucets with pressure balancing cartridge will slow down hot water when you turn handle to HOT side to prevent scalding.

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Milo