What's your pressure dropping to when the manifolds start to glow? If the pressure is dropping when it glows, then maybe you have a kinked fuel line or some other type of restriction that allows decent pressure except at higher flow rates? I had an '89 454 Crew Cab 4x4 for a while and it always got pretty hot on the hills too, even though there was nothing wrong with my fuel system. I'm not sure how well GM tuned the 454 TBI for heavy loads. I didn't keep it long enough to really dig into it, though.