our gpm is good the attachment was built to suit our excavator, the previous owner of the machine bought an aftermarket thumb and we figure when they installed it they tuned down the flow going through the hoses to the thumb, witch are now being used to run the mulching head, think we have it narrowed down to an adjustment screw on the auxiliary valve bank but i wanted to see if anyone has done it, going to try tomoroow, thank you for the reply