Could be dirt in the seal? Could be a slight bend in the ram? Could just be getting old? Could be weak return springs? I had the same problem and tried the normal fixes of cleaning ram and spraying with lubricant and then wiping down. Carried a 2x4 that I used to assist in pushing. Replaced the springs and finally replaced the two rear rams themselves. Start by extending ram, wipe down and lubricate (I used silicone spray) and be sure to wipe down again. If that doesn't help, check your return springs and if not that, rams? There should be quite a bit of advice out there on these and I hope you are a lucky one that has an easy fix.
Steve and Sheri with Archie (and Hiro, R.I.P.)
2000 Winnebago 35U, Ford F53/6.8l V10
F150 Ford and Vintage Aspencade.