727 reverse failing.

Somebody probably put the newer filter in it. That blocks the rear pump pickup. You have to cut the gauze for the rear hole. And the rule if; is you don't know that your trans is to the full mark; shut it off. I've seen one quart low burn up a trans just idling. Never warm up your trans before getting it to the full mark. Two quarts low will definitely burn it up doing that. Check forward movement for low one engine braking; if you have that, then the rear servo piston seal is okay. Check third gear; the third gear clutch pack affects reverse.