I have kind of a strange issue with my 1999 Silverado 1500 5.3L 4x4. The transmission works perfectly fine when cold. But after driving it for a few miles it almost "pops" out of gear and acts like its in neutral, even reverse is out. I have to turn the engine off and let is sit before it will go back into gear. The longer I let it sit the longer it will work for. I checked the fluid level and it is fine, but very dark. I have never heard of a failure like this, seem like a valve body issue, but IDK.

 

I suggest you change the tranny fluid and add a bottle of Lucas Transmission Fix. If that don't help you are probably headed to a tranny shop.

 

Being very famialirwith the 4l60e I never heard of this kind of issue either.How many miles are on the trans and when was the last time the fluid and filter was changed?I suggest that this be done.

 

Have someone step on the gas all of the way and check your TV cable....is it tight, like a guitar string? My 700R4 isn't an 'e', so I don't know if yours is like that but I could see a loose TV cable causing slipping when hot.

 

there is no cable on the 4L60e the down shifting is controlled by cylinoids and the actuator piston on the side of the trans.That e stands for electronic.Also if its slipping your check engine light should give you a slip code.