3 button system or 4 button?
3 button
Are all 4 tires the same make and size?
yes
Are all 4 tires worn evenly?
close
Is tire pressure equal in all 4?
yes
4WD should never be used on dry pavement. It can cause a vibration like you mentioned, which can also lead to self destruction of the transfer case
With the engine at idle, transmission in park/neutral: In 2WD there should not be any vacuum at the front axle actuator under the battery tray. In 4WD manifold vacuum must be present. When you select 2WD, vacuum should drop immediately back to zero.
it does do this but i noticed that the diaphram appears to be sucking in fully but the cable appears to only be pulling about an 1/8" maybe a little more. i read somewhere it is supposed to move 1/2-3/4". is this true? what would this do if it was only pulling the cable part way out. would this the reason the transfer case to go bad in the first place?