check your corners for obstructions...it's not uncommon for the top half to hang up on the corners....especially on the older first run cab overs. They had the guides on the front of the lower section allowing the upper frame to splay out a bit and drag against the guides. Alaskan moved the guides to the side of the lower section to aid in keeping things square as well as aligned.
Yes...air trapped in the system does fiddle with your brain...next time you change the orings....while the upper tube is out and the o-ring is being replaced...pump very slowly....I say again VERY SLOWLY.....small bubbles catch at the base of the rams...and when pushed ever so slightly will rise to the top of an open tube....ever so slowly...be patient
another thing which hangs up the movement down....loose screws which make their way out of rotted corners...once the head of a flat head screw makes its way into the path of the corner brace it will cause you grief no end.
Welcome to the obsession Gary