One reason that a shower would leak even after replacing the Delta cartridge could be because of the O rings. You may have to replace them.
Did you replace /check the seats also?
To troubleshoot a leaking Delta two-handle shower faucet, first turn off the water supply. Remove the handles and inspect the cartridges for damage. Replace any worn or damaged parts. Reassemble the faucet and test for leaks. If the issue persists, consider replacing the cartridges or seeking professional help.
The different types of Delta shower cartridges available include the Delta Monitor, Delta MultiChoice, and Delta TempAssure cartridges.
pull it or twist it
You twist the knob.
The ball very seldom is the problem it is the springs and cap washers
The different types of Delta shower valves available include pressure-balanced valves, thermostatic valves, and multi-function valves.
Delta is one of the leading faucet makers and their products are known for their exceptional quality. Their major competitors are Braun and Moen. Check out amazon.com and epinions.com for reviews.
Your Delta faucet may be leaking from the handle due to worn out seals or O-rings inside the faucet handle. These parts can degrade over time and cause leaks to occur.
If the water pressure is fine in the rest of your house. The supply pipes are either too small for how many fixtures they serve/the shower's distance from the main. However, more than likely you have galvanized pipes that are corroded and they need to be replaced with copper or pex.
Defective divertor
The warranty coverage for a Delta shower head typically includes a limited lifetime warranty against defects in materials and workmanship. This means that Delta will repair or replace the shower head if it is found to be defective during normal use. It's important to check the specific terms and conditions of the warranty for more details.