Help on 98 Aurora

Emission code PO758
When the service engine soon show the transmission won't shift.
We already replace the solenoid (Which is what that code means)
But it did not fix the problem, any help.
Sometimes it would drive with any problems for hundreds miles,
but suddenly it does it again. please share any related experiences.

when the issue happens, do the guage lights/needles cycle as if you just turned the car on?

If so, this is a very common GM problem. Its the ignition switch