well the fact that it does it when your 5ft off the floor and i'm assuming it does it consistantly in the same spot every time means you have a break in one of the wires in the mast cable most likely.
The only way to check that and verify it is to get a vom meter and check resistance/continuity on each wire and see which one is broken. High resistance or open circuit means a break in the wire generally.
Now if your lucky and the engineers thought enough in advance to add an extra unused wire like i've seen in some harnesses you can make use of that and repair it by moving that circuit to that wire.
But yes... you will need a technitian to do it if you are not familiar with that kind of work.
And furthermore... being a pallet grab problem, that is a safety issue and is imperative that it be repaired.