Yeah, I've used them with good results.
Surplus Center is a good one too.
My local Farm/Home store has a good stock of hydraulic hoses in various sizes and lengths.
My local JD dealer builds what you want.
I would put a tee in at the pump out put with a pressure gauge. Then you will know if you have a hose or cylinder or lift issue after the pump.
There is always a chance the pump is worn and binding under load. But the hyd pressure should be on the check valve and not the pump.
What happens when you take the lift to max height while the pump still running? Does the pump still run against the pressure releif?
when the check valve is closed it stops the fluid from being returned, when the release lever is engaged it allows the pressure to open the check valve to return fluid. Common failure to a check valve is the lift drifting down. Same for the lowering valve.