nasars

I have a2005 5.4 lariat changed plugs within the last 4000 miles, changed springs and boots recently I.m experiencing a loss of power/torque in the upper end of the power band. it's like part of my avaiable hp is missing. I recently towed a 5500lb camper and it was really strughling to make itbup some of the larger hills. Now I'm not talking mountains, but the rolling hills of southeast Mo. I dont havd any trouble getting up to speed, just when the engine is being stressed with a uphill load do I notice a problem. even without a trailer in place if I punch it on the interstates it seems like I 'm pushing against a thick wall of air. It's hard to explaine it seems to be trying to get more power but its just not there. Any ideas? I also have changed the fuel filter, air filter is clean and I checked the fdpm. 84000 on the clock. All fluids have been changed. Hoping for some help.

DSNY30

Same here, 05 FX4 with 95,000 miles. When I go WOT it seems like it's struggling and when I get to about 5K rpm I get a stumble and a blinking misfire CEL.

nasars

Same symptoms as mine except I not getting any cels, or fault codes per torque app. Coudd I have a partially clogged cat? Would that cause a loss of upper end power?