The way you describe it, I have a feeling this is transmission related. If you get the codes read. and it ends up being a generic trans code then see if they have a reader that will read the Separate Trans codes.
On the web I was able to find more by searching by transmission without being car specific. When I had to research I would normally find the story going "I was driving... then it shifted into neutral... wouldn't shift or stay in drive....limp mode...wouldn't stay in limp mode" The problem is there arent many solutions except "new/rebuilt trans." (I remember hoping for the Change solenoid pack solution as everything else involved dropping the Transmission and instant $$$ out of pocket) When I had mine done i was at a stop light. I also had a noise like "a playing card stuck in an oscillating fan" Once it hit a certain amount of RPMs it would shift into neurtral. Then i could shut off car turn it on and move a few feet more. ...........NEW Trans. Mechanic report claimed it was the transmission pump failed and destruction ensued.