Will a transmission out of a 1999 gmc 4x4 work in a 1999 gmc Sierra 1500 2wd
No. Not without modification. The tailshaft on the 4x4 transmission is shorter. The tail housing will bolt on and the driveshaft will slide onto the shaft but this is the slip yoke style connection and under extreme axle movement the spline/yoke can seperate causing damage. So you have a 4x4 tranny and you need a 2wd 4L60e. Well you should be able to sell the 4x4 tranny and get the 2wd one in the same condition for half the price. There are many around. It's the 4x4 ones that are getting harder to fing and the price is rising for new, used and cores.