NHTSA Complaint #11625767 — 2008 TOYOTA AVALON

I have an 08 Avalon xls and was driving and out of no where it started to shudder and it happened as I was bending a curve. I almost ran off the road. No indicators came on my dash! Because I am mechanically inclined I do know a little about vehicles! So I pulled to inspect the bottom of the transmission pan was wet! And due to the seal transmission there was no way for me to check the fluid! I believe the shudder could be from the torque converter or transmission! I took the vehicle to a friend shop and was told how to add the transmission fluid! And end up putting in a whole court of transmission fluid in before it started to show coming out where it’s supposed to be checked! By not being able to check the transmission fluid and with the shudder like it did it could have caused an accident! I still don’t know what the problem is due to the lack of money to be able to take it to a dealer to find out the true cause! And now my car shudder at 30mph and 45mph if I cruise up to the speed limit but if I accelerate faster then nothing!