Wheels are probably out of balance or you may have a bad tire.
If the rotors are warped it can cause a shake when you hit the brakes.
Tires and/or wheels out of balance?
A shake that is that speed sensitive is usually a bent rim, or bad tire.
Could be a problem with the lockup converter (overdrive).
What is 3045 rounding off to the nearest
If your truck shakes at 45 mph, most likely the wheels are out of balance. Other causes may be a bent rim or bad belt in the tire. Most of the time, shaking between 40 and 65 is due to balance. Have them check the balance in each tire first so you know where the problem is.
The truck needs a tune up.
Having a bad rod bearing could cause a truck to make a loud knocking noise and shake when driving at high speeds. The engine having a coolant leak or an engine timing problem could also cause the knocking noise.
Wheel balance
a 1500lb truck moving at 45 mph
It is 45 mph.
harmel shake