How can I adjust the operational tension of a Delta shower faucet?
The cartridge for that shower model contains all the moving pieces internally:



It isn't like some cartridges that rotate inside the faucet body.  Since the moving parts are inside the sealed unit, there's not much you can do to make it tighter.

It's possible that a low-cost replacement cartridge was used instead of a genuine OEM part.  My suggestion would be to get a name-brand Delta replacement cartridge and install that.  Since it was recently repaired, it should be an easy fix (cartridge shouldn't be stuck or anything), but you will need to turn off the water to do it.