you must have an after market reader. GM service information doesn't have a listing for p0740 on a 05 impala w/4t65e. shows for 4L trans'*. Is there a scan tool you can use that will give you data? one with bidirectional capabilities would be better. The p0742 is indicating something is going on with the tcc and being able to see the tcc release pressure pid would be helpful along being able to control it. trying to diag with out data would be throwing darts. it'* possible that the napa parts could be the issue since you didn't have this issue before you replaced the solenoid if I read things correctly. I would hate for you to go back into the trans with out any supported diagnostics.

I guess one option would be to take it to a trusted repair shop for diag and repair it yourself.I wish I had a better answer but with out knowing what is happening it would be a dart toss.