I have a 2004 F150 5.4 Fx4. My granpaw has the same exact truck. I was told that all Fx4's come with the same gear. yet his truck turns about 300 more rpm at 55 than mine does. Do they all come with the same gear and if so why does his turn more rpms than mine?????

 

Most FX4's come with the 3.73 LS, you can check by using the codes on the sticker and / or the VIN. Dunno why one would turn more than the other unless the gears were different. 300 Rpm isn't that much difference, maybe yours has the 3.55?

 

I was thinking mine had the 55's in it too. my truck has a fiberglass bed cap on it and someone told me that may make a diiference, but surely not 300 rpm????

 

The cap will have no impact on revs...only other thing i can think of is tire size..you guys running the same sizes?

 

I didnt think it would either.....

Tires on both trucks are 275/65/18

 

Can you check both you and grandpa's drivers door jamb and get the 2 number/letter code under the word AXLE. My 08 has a B6 which translates into a 3.73. Possibly one truck has had the gears changed previously by a former owner?

 

I was looking at his truck yesterday and if i'm not mistaken his does say B6. Not sure about mine. Ill have to check.

Shouldnt there be a tag on the rearend with what is suppossed to be in it????

 

The tag will have the stock ratio from when it left the factory..but if a previous owner had them changed, he wouldn't put on a new tag to indicate this.