I have a 2005 silverado with a 4.3 with a 4l60e trans. It would not shift good in third and in fourth. Pulled up codes said shift silonids so i changed them both then it goes to failsafe mode will only shift in third unless i go to 1 and then it will go but will not shift into to second or fourth. Some guy said it could be the ignition switch any help will be nice thanks for your time.

 

Not Good with tranys. But How about a filter And fluid change? Have you checked and cleaned all electrical connections? A low voltage signal may cause a sluggish shift. Hope this gives you some Ideas.

 

There was a period of time when GM trucks would drop the power circuit for the trans from the ignition switch. I think your truck maybe a little to new but it may still be possible. You need to have the power checked into the shift solenoids. You also can have the line pressure checked on the trans to see if it is an internal trans problem.