Yep mud on the inside of the wheels or a broken belt in one of the tires
does it get better at some speeds or stay the same all the time.
What speed does it start showing up.. Had a broken belt that only vibrated at 75mph below that it was fine, not noticable.. bent wheel can act that way also.. Take the wheels and have them balanced if one takes a crap load of weight that is your tire wheel causing the problem cheapest way I know of without having someone that can swap ya wheels and tires..

 

Ya my mechanic is set in it being a tire. I just don't want to spend money to replace tires if its not that. They only have about 20k miles on them. It has been getting worse since I got these tires. I have had them in for balancing and rotate. They said they didn't see anything unusual with them. My mechanic balanced them too and said he saw a hop on the two rear tires. But rotating them did not seem to change where the shaking was coming from. Also they did not put a lot of weight on any tires. It shakes at about 60+. Anything lower than that it does not shake, but I do have a slight hop on city streets probably what my mechanic saw when balancing. I might take it too a different mechanic and see what they can find. I just don't want to buy for new tires and that not be the problem. I have been scratching my head trying to figure out what it is for almost a year.

 

Your tire/wheel idea might not be to far off.

I had a really bad shake at highway speeds- would make windshield mount GPS fall off.

Was told by a reputable shop it was my driveshaft but just so happened my new rims and tires where getting put on around that time. Ended up solving it..I'm not sure if it was the tire or a bad wheel though

 

Cool I think I will go with the tires first. That would be the cheapest way. Now if I could figure out which tire/wheel it is. Thanks for the input.

 

Every now an again, my truck shakes/shimmy's at highway speeds. i can feel it in my *** and the steering wheel. it's not horrible but it shouldnt happen on a 12kmi truck. It's actually done it since 5kmi.
So, if I pull over and stop, then take off again, it will sometimes stop. This tells me that there's harmonics issue's with the frame. Once it starts, it doesn't just stop on it's own. i've sped up to 90mph when it was shaking and slowed down to 40mph and it would continue. The only cure would be to pull over to the shoulder to a dead stop and take off again.
275/60/20 stock size Cooper Zeon LTZ tires. I do have the sticky wheel weights rather than the outer edge leads but the tires are perfectly balanced. It almost feels like little flat spots in the tires, but there arent.
Also, I don't have a tow bar that connects the from frame together so that might aid with frame harmonics.

Just some food for thought.

 

That is similar to what my truck is doing. Seems like certain roads set it off more than others. But mine is 55+ I can slow down and it will stop and then speed up and it will start again. But it doesn't always do it. I take the same way to work everyday. Some days it shakes bad and some days it won't at all. You can clearly see my driver side tire wobbling/shaking when it happens. I can't see if the passenger side is doing it too. If I have a heavy enough trailer on my truck, it won't shake at all and rides like a Cadillac. But my tires feel like there are flat spots and there are none. Especially at around 35 or 40mph it feels like my rear tires are octagons. Lol. I'm about to trade the truck in. I have had it for over a year and now have 87k miles and for a year no one can tell me what is wrong.