Alright gang I have been having an issue with this since I bought my expy about a year ago, I have searched very similar threads from 2008 and on of people with the same complaint but no solutions.

2000 5.4 4x4 3.55 gears 140k miles
This thing is a gutless wonder there is no power at 50-60 mph it can't maintain it's on speed in overdrive on a small incline it downshifts. Pulling away from a stop light there is no power like it's starving for fuel until it gets to around 2700 rpm that it takes off like a turbo has kicked in.

What I've done
searched for codes none found.
New plugs Motercraft
New boots on coils
Ohm tested coils all within spec (looked like 2 have been replaced)
New throttle position sensor Spring was very weak
new DPFE sensor (old one had been broken and epoxied back together.
new fuel filter Fuel pressure within spec at idle I can't remember what it was???
cleaned MAFS and Throttle body
Checked temperature on exhaust before and after cats seamed reasonable to me so I don't think cats are plugged.

I will pull throttle body off and make sure egr passages are clean
I have an old compression tester but will need and adapter for this motor but I don't think it has low compression for the same reason I don't think fuel pump at high rpms it runs good.

I tried to tow my 12' trailer with a side x side on it last weekend and it was in second gear most of my trip trying to nurse myself home.

any ideas or help appreciated

 

Yes check the EGR system and also do a fuel pressure test.