Q: I have a 1995 chevy g30 6.5L diesel mini school bus. It wont shift into 2nd unless I floor it.

First check to see if an AAMCO warranty is in effect. Failure to shift could be caused by a faulty shift solenoid, other valve body defect, a defective clutch or clutch piston, internal hydraulic leaks and, as you know, external control faults such as potentially the throttle position sensor that you already checked. Check the fluid level just in case it is low (or too high) as incorrect fluid level can cause shift faults. If the rebuild was really recent, it would normally be under warranty. If you want a certified mechanic from YourMechanic to resolve this, the relevant service is a transmission shift diagnostic. If you request that service, the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.