2003 Jeep Liberty valve lifters

My Jeep started with a ticking sound which led to a loud banging sound. I had it towed to a ASC certified school (free labor) in exchange for allowing the instructor to use my Jeep as a teaching tool.
They replaced the valve lifters and I drove it home. After sitting in the driveway for a few hours, I started it up and the banging sound started again.
My son identified the problem as two lifters stuck and replaced them. Again, the Jeep idled great. We turned it off and it sat in the driveway for a few hours before I needed to leave, I started it up to go to town. GUESS WHAT? Do you have any suggestions why I continue to have this lifter problem.