When cooling at normal/outdoor indoor temps, the cooling coil should be 30^F below the return temp for a 50%RH interior humidity. That means 78^F, 50%RH is a 57^F dew point. A 48^F coil temp will provide significant moisture removal, you get a long run cycle. It takes 30 mins. to start removing moisture down the drain. When cooling runs are less than 30 mins., minimal moisture will be removed. During low/no cooling loads and outdoor dew points +60^F, a whole house dehumidifier is an easy fix to mainatin <50%RH. Check out the Ultra-Aire xt105H to control the home. This unit control the entire home.
If the coil temps are right, the cooling runs long, and the 50%RH is not achieved, check for duct leaks and structure air leaks.