Shaking when torque converter locks up.. possible cause?

[PiLOTLiTE]

When the converter locks in 3rd at lower mph, say between 25-30, I get a little shaking of the car. It could be described as similar to when you have a manual trans car in 1st and your rpm's aren't quite high enough, how it rocks back and forth, just not that pronounced. It doesn't seem to happen in 4th at all, or it might be so slight I don't notice it. I do have a transgo shift kit installed, but thats the only mod to the tranny. Any ideas on a solenoid I could check, or something else in the tranny I could look at?

Also, does anyone have any rebuild drawings/diagrams/pictures of the top and bottom of a 4L60-E's valve body? Would love to see some, thanks!

[chas]

well... either change your fluid (dont flush the tranmssion, just drop the pan and replace the filter and 4 qts of fluid) or try adding the correct amount of lubegard (red bottle) available at your local napa.