Well.
---- lack of pressure,---- but no mention of hydro malfunction.
---- pressure going by the piston in the ram cyl.
-----pump ( steering gear) malfunction. (not common)
The charge pump powers hydraulics, and steering has priority over the implement lift.
is the filter clean? stupid question for you I know.
if it was a constant condition, I'd put a pressure gauge on and check line pressure to the gear.
just sell it to me, as a "ran when parked" lew price

Does it get jerkey or just lack assist sometimes?
Does actuating the deck lift and holding it in the up position while malfunctioning, correct the problem?
just some ideas, others will help I'm sure.