Had a 2000 80E in a C3500 that I rebuilt that developed a shifting issue 4 months after rebuild. Once totally warm, it would start and stay in 2nd and only shift into 3rd when off throttle. It would shift right back into 2nd pressing the gas pedal. No SES. @NickTransmissions helped troubleshoot a faulty shift solenoid that was failing mechanically but not electronically. R&R'd both solenoids and truck runs just fine now; drove it for an hour and no shifting issues. Thanks for the assist Nick!