electric selector valve

I’m stumped by a hydraulic problem. I have tried to add another function to the curl circuit on my FEL for a grapple using an electric selector valve. The valve is from Surplus Center and is the valve used mainly for this purpose (third function). I have it plumbed so that the N.O. circuit operates the curl and closing a momentary S.P. switch operates the valve to switch to the grapple. Problem is: when I curl the bucket or extend the bucket the bucket operates as it should but causes the relief valve to open and the tractor engine to load hard. The bucket rolls forward and back but fluid is also going by the relief valve. The selector valve is rated for 15 GPM. My tractor is an M9000, about 85 HP and the hydraulic pump makes 17 GPM per the owner’s manual. So, what do you think? Valve to small for my application? Valve defective? Let me add that Surplus Center has been very cooperative and willing to work with me on this. The tech guy on the phone had me remove the valve, take it apart, and look for a problem. Nothing was found (trash, dirt, casting flash, ect.). When I had the valve apart I did see that the passages were only about 3/16 in diameter. Me? I think the valve is just too small and won’t handle the volume......al
Link to selector valve:
www.surpluscenter.com/item.asp?UID=2009092522304816&catname=hydraulic&qty=1&item=95117a

moderator: please move this thread if its in the wrong place....al

the selector valve has -8 input and output ports. two on one side are the inputs from FEL valve curl/dump. four on the other side, two NO and two NC. by supplying power to both solenoids at the same time should close the NO side and open the NC side at the same time. this is wired up with a NO momentry push button on the joystick. at this point i have removed the selector valve and reattached the hose with two jic/jic male adapters and the dump/curl works like it always has. ..no IR temp. gun available to me.
this vale is rated for 15 GPM. it may be the valve is rated for 15GPM in total. 7.5GPM to each circuit.....i have shipped it back...i will advise. thanks for your input....al

here is the schematic for your reference.
https://www.surpluscenter.com/Drawing/DR9-5117-a.pdf

P.S. i fixed my air conditioner! i had to buy a WSM to get it done however. i found that the dealer failed to firmly connect the expansion valve conection back on. they had to pull the connector when they installed the radio. it was just barely hanging on and only intermitly made contact. this took out the compressor relay. all is well now except for the fuel gauge. i love my tractor again now. for a while there i would have swapped it for a goat.....al