2005 Dodge Neon SXT P0700 Fault: Transmission Speed Fluctuations and Diagnostic Advice

Hello everyone, I recently encountered a serious issue with my 2005 Dodge Neon SXT. About a week ago, when I turned on the dashboard, the check engine light came on. Using a basic OBD-II scanner, I retrieved fault code P0700. The symptoms are as follows: after driving for approximately five minutes, the speedometer begins to behave erratically—fluctuating between gears, often jumping from first to second gear and reaching RPMs of 4000 or higher. At other times, the transmission fails to shift properly, causing sudden stalls or delays in gear changes. These issues occur intermittently, with some instances lasting only a few seconds while others persist for longer. I took the car to a mechanic who used a professional scan tool and advised me to perform code throws 36 and 51. They also stated that a transmission overhaul would be required, which they said involves removing the transmission housing—this process is very expensive. I’m concerned this might be an overcharge or unnecessary repair, as P0700 typically points to issues like faulty solenoids or internal transmission problems rather than full transmission failure. I'm seeking reliable advice and suggestions from experienced users on how to diagnose and fix the P0700 code in a 2005 Dodge Neon SXT without costly repairs. Any insights into possible causes, diagnostic steps, or affordable fixes would be greatly appreciated. Thank you for your time and help in reading this post.