its the pitmin arm or track bar i have seen it over an over again
Have it checked for codes. There has to be a reason that the computers are limiting you to that speed.
Probably bad u-joints in the front. Had the same.
Have you checked your tires lately are they old, need rebalanced? It also might be the steering stabalizer, the bushing do wear out after a while.
Wheel balance
With less then 20,000 miles (engine not broken in) at 65 mph, flat ground towing a jeep wrangler it gets 7.4 mpg.
If the rotors are warped it can cause a shake when you hit the brakes.
Some ideas coulb be something is lose and is just rattling or a mechanivcal problem under the hood.
I have a 1999 jeep cherokee, and had this same problem. After time, when i would hit a bump in the road my whole car would seize up and buck uncontrollably. It ended up needing two new wheel barrings. They were not easy to replace!!
problem with your transmission in 5th gear
balance tires
Tires may need to be balanced.