It's probably getting some air in the lines as well... dying even with throttle is usually that - the IP will pull fuel from the tank, even if the lift pump can't "push" it... but only if there is no air getting in the lines.
I'd be looking from the lift pump to the tank; I'd probably replace the lift pump as well; it'll help with bleeding and cranking, but will probably NOT solve your problem.
I also don't get you guys blaiming the IP... I've had plenty of sketchy, worn out IPs, and none have done that... if it were gunked up, it might respond stickily, die as you let off on the throttle from a high RPM... but flooring it will always shove things open enough to keep it from dying.
If it were really stuck tight, it would die and would never fire again.