Daveman, an easy way to check a hydraulic pump is to dead end (dead heading) a hydraulic circuit and listen for the pressure relief to unload (buzzing sound). A weak pump does not have the gpm capacity to blow the relief off. Of course, a non-visual internal leak between the pumps pressure side and sump side will also prevent pressure from rising to relief valve settings. Generally, not absolute, any pump that can blow off it's relief valve is probably ok on a gpm check.
On your loader, roll the bucket all the way back and listen for the relief valve buzz. Also, if you know where the valve is (external only) put your hand on it to feel the vibration.
For an on the fly test, when going down a mild grade rolling the bucket all the way back, on some tractors, will cause a slight tractor hold back as the hyd pump is forced to pump against the relief valve setting. This hold back can be easily felt on must small tractors.
When buying a pressure gauge, get a male coupling to match up with bucket roll back female coupling and test here. Most tractor hyd pop off pressures are between 2,000 and 2,500 psi.
Dave, after reading your second post I note the problem seems to be more with the backhoe. Don't forget, that the hoe has a pressure relief valve of it's own. If this setting is higher then the tractor setting then the tractors valve will go off before the hoe's. In fact, the back-hoe's relief valve will probably never go off. This is not a good thing with relief valves since they may stick shut if never used at all.
If pressure test at loader fails, disconnect hoe lines and retry.
If pressure good on re-try then problem could be an internal leak from pressure to sump in hoe's valve body.
By the way, backhoe digging specs are based on hoe's factory relief valve setting. If tractor setting is below hoe setting then the hoe may not be the hoe the factory specs say it is.
good luck,