Most of my experience is with 36 volt electric forklifts 4+ decades ago in the USN. But more recently (1-3 decades) I used LP-fueled ones occasionall y in moving lab machinery at the school where I taught.
In my experience, it is entirely normal for an engine driven hydraulic syst em to respond sluggishly at idle, since the pump speed is proportional to c rank speed. This results in low flow volume, and less output pressure. It was normal for me to shift to neutral and step on the gas to get faster / m ore hydraulic response from the school's forklifts. Especially loaded, the hydraulics moved quite slowly at idle. These were not high-hour machines, s o I assume they were functioning as designed.
My guess, going from minimal info, you're seeing the effect of wear on the pump and maybe valve spools. But check your fluid level, and look around fo r a spin-on hydraulic fluid filter. If there's one, replace. If you're ana l about it, send an oil sample for analysis.
You might also do a simple leak-down test. Pick up a load at at least 1/2 capacity, switch off, and see if it descends slowly. This'll give you an i dea of the general condition of the hydraulics. If it stays up reasonably w ell, you don't have much wear (but don't get under a load, ever).