[2000CAYukon]

With the gear selector in Overdrive and the tranny in 2nd gear, 1-2 Shift Solenoid is Off, 2-3 Shift Solenoid in On, the 2-4 Band is applied, forward clutch is applied and the forward sprag clutch is holding.

To shift to 3rd, the 2-3 solenoid is turned off, the 2-4 band is released, and the 3-4 clutch is applied.

If the 2-3 solenoid or 2-3 shift valve is stuck, then it would not shift into 3rd. Of course, if the 2-4 band is still being applid (servo issue) or the 3-4 clutches are burned, it also will not shift into 3rd.

From 3rd to 4th, the 2-4 band is applied, the forward sprag clutch is released and the 3-4 clutch should still be held.

Is the check engine light on? A bad solenoid or shift valve should set the light. Not sure if bad 3-4 clutches will set the light.

//2000CAYukon