Hey guys i have a vibration issue on my 91 s15 jimmy 4x4. when im driving in city speeds i do not get any vibration when i drive at highway speeds 55-70 mph i get vibration. Now when it starts to vibrate and i press the gas a bit it goes away same when i step on the brake. I dont know exactly where the vibration is cant really tell its a 2 door. so kinda sitting in the middle. Since im here anyways my 4x4 also wont engage i put in 4 low 4 high nothing i have no idea on how to check these things this is my first 4x4 vehicle kinda new to blazer/jimmy trucks.