If your shower pressure fades away rather than staying steady, the problem may not be the shower at all.
On a well, check the system first
A pressure tank that has lost its air charge, or a pump struggling, shows up in the shower before anywhere else because that is where you notice it. Before replacing a perfectly good shower valve, it is worth ruling that out — and we would rather check it than sell you a valve you did not need.
Iron staining
Orange staining on tiles and fittings is iron in the well water rather than anything wrong with the shower. Cleaning helps for a while; treating the water is what actually stops it.
You may not need to lose the tile
Many valve repairs are reached through the existing trim plate or a small opening in the wall behind. Before agreeing to a quote that involves removing tile, it is reasonable to ask whether the valve can be reached from behind.
Sediment in the cartridge
Well water carries fine grit that works into mixing valves and stops them sealing. Replacing the cartridge restores it, and a sediment filter stops it happening again on the same schedule.