99 4l60e change to Dexron VI troubles

[carlprop]

I had my 4L60E rebuilt 2 years ago. I asked the transmission shop about using Dexron VI in it. They showed me a thick book on ATF used in different cars.

They put in Dexron III and Lubegard the red bottle in it. It does have very firm shifts from 1st to 2nd. As in a previous post, I do get that forward lurch every so often when I first start it. However, it only happens if I let it sit overnight.

 

[Ramblin Fever]

I have the 4L30 which is the slightly smaller brother to the 4L60, a year or so back I did a drain/refill i.e. 4qts of Dex/Merc Valvoline Maxlife fluid into the mixture of Castrol Import Dex 3 atf. It drastically changed the shift characteristic of 2-3rd gear, however, it made the shift rougher.

Didn't like it at all; I dumped 4qts out and refilled with my long-standing favorite castrol import atf, shifts smooth as butter.

I DO believe shift quality changes from one brand to another for sure; I have yet, and will not try Dex 6 in this tranny...at least if I can prevent it.