rvmercer

4L60e operates nicely when cold, but once it warms up, first and reverse are really sluggish. Feels like I need to give both a little throttle to get rolling.

Again, works pretty normally when I drive it on a cold start, but after a few minutes it degrades.

Any thoughts appreciated.

Thanks.

Thomas Elliott

How many miles on it? Recent fluid changes from one type or brand to another? What year model vehicle is it in?

mrvedit

Check the fluid level, which is done properly with the engine running.
If fluid level is OK, there is a more serious problem.

When the trans is cold, line pressure is higher because the fluid is thicker.
As the trans warms up, the fluid thins to it normal level and pressure drops.

Connecting a pressure gauge to the trans would be a very useful diagnostic step.

As hinted above, if it has many miles, it is simply worn out.