Vehicle Shaking between 60-70mph..HELP!

Ok so I am getting a bit irritated at this current issue and could use some input and suggestions on what route to take next. I drive an 04 4.0 eddie bauer with 115k on the clock. A couple months ago I went from the stock goodyear fortera's to the same size Goodyear Wrangler Silent Armor's. Love the tires and they are exactly what I need in winters and driving on muddy access roads. Tires perform GREAT between 0-55 mph, but when on the highway and the needle starts to hit 60mph i can feel a shake in the wheel, and throughout the whole truck. Passengers can feel it as well when riding in the truck. It is the worst at about 66 mph then when it gets towards 70-75 it gets much better. I have had the tires balanced 4 times, Truck aligned, everything on the front end checked by a mechanic and he says nothing is wrong and said I may have gotten defective tires. That would just be my luck! I dont know if this would cause any shaking but i had a CV boot on my front axle leaking a bit of grease about 8k miles ago and i sealed it up good and it hasnt been leaking since, but could it possibly be a bad axle? Thats the only thing I can think of right now. Any ideas, suggestions and anything I havnt tried yet that people can think of would help a lot! I drive 50 miles/day on the highway for work and it just drives me nuts!!!! Also, this is a strange observation but during colder temps (0-35 degrees) it seems to shake worse than when its 60. So the warmer the temp the smoother the ride. Just weird. Thanks!

4x4?

http://www.revbase.com/BBBMotor/TSb/DownloadPdf?id=127021

hmm, yes it is 4x4. I have been doing research and it could be SO many different things im almost just willing to live with the shake rather than dish out thousands of dollars chasing it. This explorer already has 9k+ in repairs and is finally paid off but id like to enjoy driving a paid off vehicle for a while!! Problem only happened when i bought the new tires...