Why is my truck shaking?

Do you mean shaking while driving or the engine is vibrating when the truck is standing still? Why on earth would you suspect the starter as causing that? If the engine is vibrating when the truck is not moving, and it got worse after replacing the spark plugs, you have two or more of the spark plug wires mixed up.

Idling? Driving? Idling: Check timing and air filter. Check for vacuum leaks.
Driving: Probably wheel balance issue.

Answered in other thread. Timing probably if the engine is shaking. Vacuum leaks. Wheel balance if while driving.

The truck was not shaking before. We were having issues starting the truck is why we changed the started.

It is shaking while driving and at red lights.

while driving is most likely a wheel balance issue. While idling is most likely either timing, vacuum, or switched plug wires.

See my last answer.

Ok thank you

At red light? then may be you have crossed a few leads over, and you have a misfire, i would be checking this first.