so i have a 2002 f150xl sport reg cab 4.2l v6 5 speed.

everything runs perfect and what not, never had problems.

only thing i ever notice is on the highway, when driving from 70-75 my truck shakes like crazy. shifter **** goin all over the place, anything in cupholders going balistic. everything rattles. its terrible

as soon as i hit somewhere around 76+ it goes away. i cant for the life of me figure out why this is? any clues?

 

Try balancing youre tires

 

Could be tire/wheels need to be balanced, or you might very well have a U-joint on the driveshaft needing replacement, if so don't let it go that way very long, those bad vibrations can wreck some havoc to your transmission internals as well as your morning coffee.
Good luck.

Kevin.

 

ill second the morning coffee notion, but why would it only be through that small 70-75mph range?

 

Idk my gfs saturn shook during certain speeds and it just needed to be balanced

 

On my Ranger I had a similar issue, only it was between 40 and 45mph. Ended up being an out of balance tire. Have your tires balanced and see if it helps.

 

If you have a limited slip differential they sometimes act up. Happened to my 2000 4.6L 2wd from 55-60mph. To fix this all u need is to hange the rear differential fluid and add fricyion modifier.

 

balance your tires, check U-joints, and check to see if there's any play in your wheel bearings.

 

Its a harmonics thing. It just gets to the point where you cant feel it (kinda) really hard to explain. I would pull the tires and inspect them, look for a spot that a weight may have come of or a rock in the tread. It will only take about 3 grams to offset a wheels balance. When you put the wheels on make sure to get the lugs tight.

 

Thanks everyone. I need new tires but I decided to rotate them and since then it's been fine