OK I need a little help diagnosing an issue I'm having with my 4L80e trans

I recently rebuilt this 99 core with Jakes rebuild kit. The trans had been performing flawlessly for a few months up until recently.

Sometimes but not all the time when shifting into reverse or drive from park their is a 2-3 second delay engaging.

Also when the trans has had time to cool overnight and I mildly accelerate I get a quick slip into neutral then back into gear. It doesn't seem to be consistent with any gear/clutch pack.
It will only do this once then be perfect the rest of the day.

The trans is able to hold WOT shifts in every gear and shifts just as firm as it always has.

Does anyone have any ideas before I try too hook up a pressure gauge to this thing?

Would a Boost valve sticking cause this??

 

Sounds like either a low fluid condition or a pump failing.

 

Well darn, I know its not a low fluid condition since I just checked and corrected a slight overfill.

I guess I will pull the pan and take a look at the filter.

 

Yeah look at the filter, check the filter to case seal, and be sure the VB is tight, etc.

 

just got home after a long drive and all was good but if I shut the car off and wait a little then restart I get the delay shifting out of park. Only that one time then its perfect.

 

I had this problem after my build but I think I forgot to remove the reverse check ball? After I removed it all was well.

 

Good to know but this problem did not show up immediately after the rebuild, it was functioning correctly up until recently.

As soon as I can get it on the lift I will pull the pan and report back.