590SM fuel issues

My 590SM runs very good until I push it or load it up. When I try to dig into a pile of dirt and give it more fuel it bogs down and starts to stutter even when I back off and sometimes stalls. If I use a lower gear 1 or 2 and let the momentum of the machine dig into the pile, I can scoop it up and dump it in my dump truck. When it does bog down I either have to shut down the machine and wait about 30 sec then restart and all is well or sometimes I have to shut it down and loosen the fuel connection at the injector pump after the fuel filter and pump the fuel pump to get out air. After that it starts fine until I push it again. I replaced the fuel pump, fuel filter, fuel line from the pump to the tank, removed the pick up assembly from the tank and checked for debris or a blockage but all seems fine. No smoke, black or white when it happens. It just seems that it is starving for fuel. Is it possible that they sold me a bad fuel pump? When it's running good I can tack it out at 2300 and hold it there with no problems - it's only under load that this happens.

Anyone ever have this problem or have any ideas?

590SM fuel issues