1999 Saturn SL2 with P0731, P0732, P0733, P0734 Codes - Speedometer Sticking and Hot-Weather Reverse Issues

My 1999 Saturn SL2 has over 114,000 miles. Since reaching approximately 95,000 miles, the speedometer has been known to stick when coming to a stop—displaying whatever value it last registered (e.g., 30 mph) and refusing to reset properly. After my last transmission fluid change about one month ago, I noticed the car would sometimes slam into reverse, but only under extreme heat conditions. This week, the Service Engine Light activated and triggered several transmission-related diagnostic codes: P0731, P0-732, P0733, and P0734. My owner's manual provides incorrect gear ratios for gears 1 through 4, which makes troubleshooting difficult. The car shifts normally under normal conditions, but when the check engine light is on, it begins to rev higher—shifting from around 2500 RPMs to approximately 3500 RPMs. This behavior only occurs when the light is active and seems to worsen in hot weather. I'm seeking advice on how to interpret these codes and whether a transmission repair or fluid flush might resolve the issue.