My manual override has so much pressure on it that I cannot manipulate the pump by hand. Any thoughts ?

Orca, sounds like you have a major bind somewhere in the system Could be at the cylinder, especially if it hasn't moved in a long while. Sounds dumb, but a sharp smack with a hammer on the end plate (where all 4 cables are) at the end of the piston. Somewhere it's jammed. CAUTION, if you DO free it with pressure in the system, it'll move! You don't want any of YOU in the way. Not uncommon for a piston to freeze up from disuse. Let us know.
Tree

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Treeclimber
2703 Tow Lite
2002 Escalade
Bonita Springs, Fl. &
Andrews, NC

Orca; My guess is the manual pump is stuck from nonuse an it takes a lot of force to get it to move. Hit the jack handle hard with your hand or a light rep with a hammer to break it loose. The owners manual does not tell what pressure the pump is set to to raise the top. My guess is that it is different for each trailer length/weight of the top but over 1000psi. The pump can put out upwards of 3000psi. To raise the top manually it takes a lot of arm strength and the manual says aprox 140 pumps on the jack handle at a force of 40 foot pounds. The manual also has a caution not to over exert yourself doing this. As Tree said you could have a bind between the top and bottom or cable system. My bet is on a stuck manual pump. Read my answer to a post today under the heading "hydraulic lift system" for more info.

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Jim L & Faye
2805C
2003 Silvarado diesel crew cab
2017 Silvarado, crew cab 1500 6.2L gas w/ 8 speed tranny
central VA