Hey guys,
I have been having an issue with my 4l60e that i had built a few months back. I have all red alto clutches numerous upgrades including pinless pistons pretty much everything short of having better shafts and a transbrake. But anyways ive had zero issues till the past few days. it had been sitting for a few days and i went to drive it , put it in drive and it would rev really high before it would move the car. I checked the fluid,yes with it running, and it checked ok. Put it in reverse and felt fine. then i go to drive it and it seemed fine till i got on the highway and 4th kind felt funky like it was slipping . So i went easy on it and parked it when i got to work. On my way home it now doesnt shift into fourth at all and isnt locking up. Im really thinking something is either stuck somewhere or maybe some debris is blocking something.

What do you think could be causing this? How can i diagnose this while in the car?