[Ssherwood]

My duramax started to not want to shift properly. When i put it in drive its goes first but pops out sometimes then from first to second then stays in second until i go to neutral then back to drive then it goes to fourth and stays in fourth until i turn the truck off. I thought it might be the nsbu switch or a solenoid but im not sure

 

[Ssherwood]

Please help driving to work in 4th on the hwy has tripled my fuel consumption lol
And it being built its already not the best on fuel

 

[Jasong]

Have you changed the fluid?
It sounds either low or a clogged filter.