Weak water pressure

We've had weak water pressure in our upstairs master bath shower ever since we moved in over 5 years ago. The guest bath also upstairs has plenty of pressure, and has the same Delta setup. I've tried different showerheads, but it doesn't help.

To complicate matters, it started leaking from the showerhead, and I fixed it. While learning to fix it, I twisted the supply lines a bit, which I thought would make the pressure even worse -- but to my suprise, it's the same. I guess my question is now two-fold:

(1) Should I be concerned about the twisted supply lines eventually breaking, and flooding my house;

(2) How do I increase the pressure?

I guess (1) takes a backseat now to (2).

Thanks.

(1) YES. This particular Delta design has been the bane of many plumbers and homeowners alike. ( Most plumbers are quick learners and only make the mistake once, early in their career!).

(2) Have you removed the shower head itself to see if you get good flow just right out of the pipe? If not, then something may be lodged inside the valve body. You could try to blow it out by turning off the mains, taking apart the body, and connecting a garden hose from outside, or compressed air, to the shower arm.

Given both issues, it might be time to start looking for access to replace the whole valve. By the way, the new Delta R10000 rough in valve has eliminated the problem of the tubes, and also the problem of the nut being stuck which is how the tubes become damaged.

Thank you Jimbo. I switched the showerhead from our good bath, but still had poor pressure. Do you mean connect the garden house to the showerarm, and running water back down the supply pipe? I didn't think that was possible.

I replaced the whole cartridge last time, so that part is clean. I'm still a little worried that the supply lines will break in the middle of the night, or while I'm on vacation. I can't really tell how much I twisted them, but if it's not leaking now, am I really safe?

I'd probably need a plumber to replace the valve, and I'd like to avoid the expense.