It could be. Are you able to get part numbers off of the load control valve?
The procedure described in the manual is a good way to field-set a counterbalance valve. Need to ensure that this is done with slightly greater than expected load on the valve... So if you're normally lifting a person and some stuff, set the valve with a person, some stuff, and a little more stuff.
The counterbalance valve is essentially a lockout/relief. If the pressure induced on it by the load (the boom, basket, people, supplies) is higher than the setting, the valve will open and drift down. That's why they say to set with the boom all the way out and someone in the basket. To put a higher load on it than it would see under normal operation. This ensures that it won't drift down unless it's overloaded.
Where CBV's get fun is in the pilot ratio. If you have a valve with a low pilot ratio, and it's set too high to begin with, the pressure the pump has to make to get it to open increases.
To make matters worse, the pilot pressure required also has to overcome back pressure in the return line at a 1:1 ratio. The way the flow control is plumbed between the CBV and the control valve, and in a 'meter-out' (controls flow on descent, not raise) the pressure drop over that flow control is directly additive...so things start to pile up, so to speak.
All these factors are why your machine appears to be 'laboriously driving' the boom down, rather than just controlling it's descent.