Shaking when i reach the spead of 40-60 it shakes and vibrates and then goes away after reached higher speeds does the same thing when slowing down

Unbalenced wheels..Bad tiresBefore 80 is too slow it will shake and wave and vibrate.After it can stabilise or get worse.Last:bad motor sensors:air intake,valve timing etc. If not ruff acceleration (rpm related vibration) then is the wheels related (unbalanced,bad/defect tires,low air pressure,loose nuts...)A windy weather also shakes u well :)))Cheers.

sounds like a worn out transmission mount try rocking the ****** up and down and if the play in the rubber mount appears excessive this can cause all of the stated problems

wheel balance?

sounds like a bad u joint or swing bearing or just something loose in thr drive train

Tire balance is likely cause, It starts shaking at a certain speed then will stop at a higher speed, If it were a bad belt it would have a constant wobble feel

Hi:
This just my best guess, but the only time I had a vehicle behave like that, the lock up torque converter was not releasing properly. My car was a Chrysler, and The torque converter lock up solenoid was to blame, and it could be the same thing for you.

Get your tyres balanced, makes a HUGE difference and the tyres last longer too.

Could be your torque converter.
Have you checked all your fluids?
How is your oil Pressure at that speed it should be between 40 and 60
Any Check engine Light?
Does your Abs lights come on?

it could be a motor mount check the condition of it or it can be that something with the suspension might need attention . . those things can cause vibration at certain speeds

seems like there might be something goin on with your suspension