when going down the highway once i reach speeds of 65+ my truck vibrates like CRAZY! i dont know wat it is the whole truck feels like its going to fall apart only at speeds 65+ tho any ideas

 

Have you fixed your plenum and clogged cat? Mine would misfire on cylinder #8 and combined with a clogging/clogged cat it would shake real bad at 45Mph, so much I couldn't go any faster then 45.

Also another thing to consider is are your wheels/tires all in balance?

 

plenum hasnt been fixed yet doing it in the summer wen its warm i dont think its that bad yet anyways because i dont burn oil and still have power ...the tires were balanced 15000miles ago wen i got new ones

 

Hit anything that might of bent a rim? Possible bad u-joints in the driveline.. Crawl under and take a looky loo and poke around.

 

You could pull your #8 plug and take a look, or take off your throttle body and have a look in the intake.

Either a clogged cat or misfire is the only thing I can think of motor wise. I suppose it's possible it could be something with the transmission if everything else checks out.

Quick test, next time you plan to be highway at highways speeds take out your pre-cat O2 sensor and see if it runs any better. Removing the sensor temporarily will release some of the pressure in the cat if it's clogged up.

 

sounds like a bent rim, horribly unbalanced tire, u-joints, or a bad alignment. when was the last time you had your tires rebalanced and rotated?

 

stewie if it only at highway speeds then it doesnt sound like a clogged cat to me. correct me if im wrong, but wouldnt it would show symptoms in all fourgears everytime he hit the gas pedal when under load. not just at highway speed.

 

You're probably right. I was using my experience as something to go by. But it was also misfiring too, but I really couldn't tell it was till 2 days of that crap before it threw a code.

I couldn't get past 45 and it would only shake at 45. But that's just my personal experience.

I kinda think it may be a bent rim or out of balance tire.

I've never had an alignment issue cause a shake. And I've had alignment's pretty bad outta wack, enough to eat clean through one side of the tire

 

i got new tires 15000 miles ago and they were balanced and rotated then and i dont recall hitting anything that would have bent a rim

 

It's still possible a wheel weight could have come off, take a walk around your truck and check for missing wheel weights.