I agree with everyone about putting it back to stock. That could also help rule out the aftermarket parts didn't cause it. On the HPFP, it's possible but when my pump failed the car was running horribly rough, like on one or two cylinders. It also took a long time to start so to me it doesn't sound like fuel pump problem I had. I believe limp mode is triggered by something that could damage the motor like overheating, over-lean condition, detonation, etc. The dealer is your best bet but take it in stock.