2009 Aveo5 Won't shift into top gear; no codes

a mechanic already reprogrammed the transmission computer and no luck. He said I could try replacing the computer, but I thought I might try some other things first.
Had a pile of troubles with this one and a lot of them started around the time I had a transmission flush at another mechanic.

Basically runs fine now, but the revs just keep climbing and no shift no matter how I drive after hitting 50mph.

67k miles, kept up with most regular maintenance, haven't recieved any recall notices.

Any chance a second trans flush might fix it?

Do you have a scan tool that can show you your transmission fluid temperature as you drive? If the transmission fluid temperature sensor is sending too low of a temperature, the transmission computer will prevent the final shift in order to prevent damage.

thanks for the tip!
I donn't have a scan tool, but I'll see if I can wrangle one.