When opening a valve completely at low idle, the engine stalls due to pump upstroking and demand on the engine. Partial opening or slow opening of a valve will not stall the engine at low idle. This applies to all valves, loader and hoe. The engine really needs 1500+ RPM to not stall when opening a valve. I have never encountered this type behavior on other machines. Is this normal?
no, there's a valve on the pump called the "Torque Limiter" that normally limits input torque. If the engine is otherwise running well and making good power, there could be an issue with the TL or the other pump controls. To set the TL properly requires a flow meter, but some Cat guys had a "field adjustment" they would make by running the Air Conditioning, and all the lights etc and then steer hard at idle and then set the TL to where the engine wouldn't stall. It's not a DIY adjustment though - requires some experience with load sensing hydraulics to set it all up.