9" rears dragging

If it’s both rear brakes it’s most likely the master cylinder OR the rear brake hose. Just because the rear hose is new doesn’t mean it’s good, there have been issues with brand new rear hoses with inner linings that close up.

It’s also possible it’s the wheel cylinders, but, those are independent so it would be less likely that both are bad and yielding the exact same problem on both sides at the same time.