Class 3 carriage, with a full free triple, secondary's hitting hard when they fully seat. Free lift cylinder of course is at the top of the stroke when secondary's start to raise, if I lift it 6 feet or 6 inches it slams when they come down, removed both secondary's for inspection, solid rod, no check valve inside either cylinder, looked good inside of barrel, re packed and reinstalled, replaced flow protection valve and lowering valve. Still slams, seems like return to tank is not restricting return flow. Checked for rails hitting something, not seeing any obstruction anywhere. Sounds like the cylinders are bottoming out. no cushion at all, just slamming, customer says it's been doing it for years. Any thoughts???