I've noticed when I'm just driving normally the truck shifts fine from 1-2, 2-3, but then when it gets to the 3-4 shift, it seems like it shifts, goes back into 3rd, then shifts again back into 4th. it seems to shift fine. It went from doing this occasionally, to doing it nearly every shift from 3-4.
What could be causing it to do this?

 

Sounds like torque converter lock up to me. Basically you shift 3-4 then your coverter locks and feels like another shift as the RPMs drop.

Does that sound right?

 

I have been having problems with my transmission doing the same thing.
I have a rebuilt 4l60e. They rebuilt it using factory parts thou but i had the guy at the shop put me in a custom valve body. It shifts hard between the 1-2 shift. The 3-4 shift has me scared doesnt feel like it wants to go into 4th gear sometimes. Im just going to let her eat until it explodes again.

 

No , I can be in 4th gear and running fine but if I let off the gas and then give it gas it acts like it is going to downshift, the RPM's go up but then it goes back into gear and does fine.

 

Like Hitman Said Tc Lockup

 

What causes that? What is the fix?

 

THIS IS NORMAL

 

It's there so you don't need a full kickdown to accelerate I'd assume. It's normal and what you want.