3-point lift arm control extremely stiff

[UncleBuck1]

The position control on my MF2660 takes a lot of force to operate- it's so stiff that I can't work the lever while sitting in the seat. I thought maybe the control lever pivot was too tight and sticking so I disconnected it but it moves freely, so apparently it is either the input shaft or something internal in the lift system.

Can anyone give me some guidance on how to go about finding the problem?