Did a little research over the weekend since I installed my coolant filter kit (NAPA #4019) and had a waterfall of green antifreeze pour outta the lines "DAMM!T" Thanks previous owner. Not trying to advertise on here but hopefully this will help someone since I work for a Ford Dealer with a NAPA...
Just as an example I work in a "FORD DEALERSHIP!" and maybe 2 people here besides myself are aware of the importance of a coolant filter on a 6.0 but we have 9 "Techs"
Well I bought my first 6.0 a week ago with 270k miles on it and I love it. Today it received a 4" straight pipe exhaust which I'm very pleased with. I've ordered a coolant filter kit, Head studs, oil cooler, egr delete, sct 3015, and I'll buy head gaskets soon since I work at a ford dealer they...
Just based off the description vs symptoms I would lean more toward the lift pump starving out somewhat explaining the power at high rpm but dead at low rpm, I'm basing this off of more experience with these results in an old IDI but the principles are still the same Rich=low end torque lean=...