Lately, it really feels like my '01 5.4L Screw is really dragging, especially in first gear. It feels like it takes 20 seconds to get all the way through first gear, then the shift at the top of first (at full throttle) takes another hour or two (alright, maybe I'm exaggerating just a little). Maybe I'm just picky, but it just seems a little slow to me. Seems like it has dropped off lately, but I haven't changed anything. I recently ran some fuel injector cleaner through it and just for the gas tank that I added it to it seemed to have 50 more hp (leading me to believe it is the engine rather than the transmission.)

The truck has 206,000 miles on it, so I don't expect it to be 100%. It seems to run very smooth... no unexplained shakes, shimmys, or noises.

I intend to have the tranny flushed and a new filter installed for it. I don't know if this is more likely to be an engine or transmission problem (or TC?) but any input is appreciated.

 

Change the fuel filter, and take it to a muffler shop to get the cats tested for blockage.

 

Wouldn't a clogged cat be killing my mileage though?

Just put a new fuel filter in about 7,000 miles ago.