shower diverter valve is now hard to activate

. . . after I replaced the showerhead with a showerholder with a metal hose and a handshower. I have one of those Delta tub faucets with a diverter actuator handle at the end of the tap: pull it up for the shower - down for the tub. With water at full pressure, it is now much harder (but still possible) to pull the handle up for the shower. I also need to apply more pressure to force it back into the tub position. With water at half the pressure - no problem. I suspect because of my shower installation, it is harder to force the water to shift from the tub to the shower position, but I do not understand why.
I removed small o-ring mesh filter, check valve, and flow restricter from the shower unit. I think it got a bit better but not by much. I still need to see what happens if I disconnect the metal hose form the showerholder base - it is a bit tricky and I am not up to this challenge at the moment.
I would appreciate an advice.
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