It may be the diverter that is causing the problem.
Do you have the original paperwork that came with the faucet?
It is a Home Depot House Brand and all roads in research lead to Home Depot. These most often are Chinese faucets and without the original paperwork figuring out exactly which part number you need can be fun.
Personally I would rip it out and install a Delta or, Moen faucet in its place.
You can talk to smockman at 1-888-328-2383. Maybe you will get lucky and talk to someone there that can help you.