Transmission doesnt engage at low rpm, any advice will help Options

[rapid36]

Hello everyone my celica has been running great for years after my rebuild and i always had a running rich check engine light. I recently now am having troubles sometimes but NOT ALWAYS engaging into a gear from either a dead stop and trying to go again or shifting into a new gear. Seems like when im going and driving it doesnt have any issues going into any gears but from a dead stop it sometimes wont get into the gear unless I rev up to about 1.5k-2k super embarassing at stop lights as you can imagine. Any advice would be appreciated. Let me know what you guys think that I can start checking.

Things I have checked.
Transmission fluid is full and havent had to add any.
No new check engine lights or codes.

Thanks for your time!

[Box]

Most automatics have a metal and mesh/foam filter that goes into the valve body. Which if it was rebuilt it's possible they didn't get the clutch friction spacing right and it's burning itself up... Check the fluid for grit or burnt smell. You might want to contact the rebuilder if there's a warranty it's still within and voice concern. It's also possible that solenoids or something in the valve body is sticking. This is why I don't like automatics, they're full of black magic.