1999 Camaro 5.7L. I just recently rebuilt by 4l60e. I was having hard 1-2 shifts and when going over 45mph some times after a short coast i would get neutral untill I shifted down to D or tapped the brakes. Rebuild included pin less accumulators for all 3. 3-4 zpack frictions. The beast shell and other replace Everytime parts and the transmission bench rebuild kit. Everything seems to work perfectly but I just got the neutral after coast. I was going around 68 mph and cruse started jumping around like before. Deactivated cruse and after a short coast I would get neutral unless i braked or hit the gas then it grabbed like normal and I was back in business. It's accelerates fine and I have no other slipping that I know of.

 

Sounds like a fluid level issue

 

I'll double check fluid level but it isn't consistent. Last time it only happened after about 1.5 hour drive at highway speeds. But before rebuild I could make it happen with short trips but only after coasting doesn't mess up when accelerating

 

So you were experiencing this before rebuild?

 

Yes it was part of the reason I rebuilt it. But it was more prevalent before I also had the harsh 1-2 but it was clear the plastic accumulator was cracked around the pin.
I have about 800 miles since rebuild and it's happened once on a longer trip 1.5 hours.

 

Did you change converters or use the previous?

 

New factory style converter from advance auto. My initial thought was the tcc valve I put the spring from the rebuild kit in it to delete the PWM but the plug did show wear on it the car has 135k miles. So I was thinking I had fluid leak around the valve. So I got the sonax reamer and valve but waiting for it to be delivered. I wasn't sure that would cause my symptoms though.