I just started noticing an issue with my 2001 blazer ls 4x4. While driving to and from work ive been noticing a shifting issue around 45-50mph. Starting right around 45mph the truck seems like it almost doesn't know what gear it wants to be in. It will feel like it wants to kick down and then jump back up. It will do this with the gas held steady in one position and doesn't rev super high or anything. Simply put it feels like it doesn't know exactly what it wants to do. The truck seems to shift and drive fine in every other gear and situation.

Any help on this one would be greatly appreciated!

I drove home tonight and tried to pay closer attention to the issue. When the truck is trying to figure out what gear it should be in it is only changing rpm by about 300 or so. Do these trucks have a built in overdrive at all?

 

With the automatic 4th gear "D" is overdrive. 45-50 mph is right at the shifting point, so you need to back to 40 or bump to 50 for it to want to hold its gear.