Haveing a on going issue

[agnt549]

have a 03 H2 it runs fine when i first get it out and then when it gets hot i lose power i can have the gas pedal to the floor and only get like 1k rpm if i stay on it it will open up it does it on flat ground hills down hills ! have put new cats, muffler, throttle body, plugs & wires, coil packs nox sensors with plugs and radiator I'm at a lost HELP