Transmission wont go past 1st gear

Hello, my idea is that you have an internal transmission concern being that you have a ton of miles (relative to the vehicle and transmission life expectancy) and if it will not shift, this electronically operated transmission likely has an internal mechanical concern. Hands on testing and monitoring internal component function with a diagnostic tool is definitely the next step, as well as making sure the transmission fluid is full and clean -- but I expect ultimately an internal concern that is prohibitive to fix and will require overhaul or replacement.