My 00 Chevy z71 will not shift out of 2nd it never started slipping or showed any signs of any kind of problem so I dropped tha transfer case and I found one main red wire that has been pinched or cut then I found alot of dirt in one of the speed sensors and also noticed that bc of the dirt the plug wasnt connected to the speed sensor.so with one unhooked speed sensor and a pinched wire will this cause the transmission not to shift out of2nd

SOURCE: Chevy Transfer Case

The most common thing to go wrong with chevy transfercase is the rear tailshaft has a snap ring that breakes. Just remove the bolts holding it on and inspect the shaft and see if the snap ring is broken.Then just replace it with a new on from the dealer.

SOURCE: 1998 chevy k1500 4x4 4

first of all your truck is already in first gear when your going down the road....lol

SOURCE: chevy transmission hangs in 2nd,

It just holds 2nd forever. Is the 1-2 shift point high?

SOURCE: Need to change the transmission filter in '99 chevy suburban 2wd.

If it has over 100,000 miles or so, don't do a complete fluid exchange. Drop the pan, change the filter, and add 2 bottles of Lucas trans. additive. No premises but it's better than a new trans. Worth a try.

SOURCE: 1995 Chevy 1500 Z71...transmission only shifts

It sounds like a vacumm modulator issue.