F150 5.4 loss of power when accelerating

Feels like I'm dragging something behind me. Almost like something is tugging me and lets me go most of the time. I'm getting 14mpg & 8mpg when hauling my boat. The previous owner must have had a chip or something mounted on the dash. I'm sure he hauled things as well but feels like I'm getting terrible performance.
Ive changed fuel filter, flushed the fuel system, flushed radiator, but nothing major yet.. Any suggestions???
Thanks in advance

have you checked the timing? also pull plugs out and check the gap it should be under hood on gap. another thing you may want to check e-brake see if there working wright. do you no when the last time 0-2 sensors been changed? some more thing's i can think of is checking all vaccumme hoses. and run some seam foam threw your gas and make sure your air presure on your tires what your truck calls for and don't go by what it sais on tires run what it calls for on truck witch should be on drivers side door. and cat converter can be pluging up also.

good luck.....

Sea foam is ok, I agree alot with exhaust. I disagree 1000000% on the tires though, DO NOT go by the door sticker, that is the cause of the firestone/explorer fiasco a few years back. Ford had less air in them than the tires were supposed to have. The door stickers are for ride comfort, go with the tire print, and keep in mind, MAX load is Also at MAX pressure, somewhere in between the max and the door is ideal.

you didnt say anything about the fuel pump, id check that...

Also check your catalytic converters . My '96 F150 had no power when I bought it ( used ). I replaced the dist. cap , plugs & wires , fuel filter , PCV valve and cleaned the IAC , MAF , and throttle body and nothing helped ! Finally I had the front cat . converter replaced and removed the second California only required cat. removed and replaced with a straight pipe ( they looked new on the outside but the front cat had disintergrated and plugged up the second cat ) and it made a world of difference in the way the truck runs ! Might not be your problem but worth checking ! Good luck !

How is your catalytic converter? This can be a symptom of the converter plugging up. Is there a rotten egg/sulfur smell coming out the exhaust?