2005 Jeep Liberty Diesel P0218 and P0173: Low Power, Limp Mode, Transmission Not Downshifting

My 2005 Jeep Liberty diesel is experiencing significant performance issues during acceleration, hill climbing, and passing. The vehicle appears to be in limp mode, with the transmission failing to downshift on its own. This issue began approximately two weeks ago, and since then, the 'Check Engine' light has been the only warning illuminated on the dashboard—there is no 'No Trans' or overheat indicator. I have already inspected the wire harness, TCM, ECU, and ground connections—all show no visible damage. The transmission has 183,000 miles on it, originally installed when the vehicle was purchased in 2006 with only 35,000 miles. I’ve maintained the vehicle diligently over the years: regular oil changes, brake services, and all maintenance tasks were performed per factory recommendations. The transmission service was completed three times during prior ownership, including at 155,000 miles using Valvoline ATF+4 transmission fluid and NAPA filters. The only time the transmission overheating light activated was about four months ago while towing a heavy load over a steep hill. I immediately pulled over and let the engine idle in neutral until the warning light extinguished. Since then, no further heavy loads have been attempted. The transmission dipstick reading shows warm fluid (not hot), and the trans cooler lines are warm to touch—though not hot enough to burn—but this warmth suggests fluid flow. I am currently seeing two diagnostic trouble codes: P0218 (Transmission Temperature Sensor Circuit Malfunction) and P0173 (Rich Fuel Mix in Bank 1). I suspect a faulty solenoid pack, as the internal temperature sensor may be affecting signal routing to the speed sensors. However, I'm concerned that a defective speed sensor might not generate any related diagnostic codes—especially since the transmission temperature signal appears to pass through both speed sensors before reaching the TCM. Given this, I’d like input from others who have experienced similar symptoms on 2005 Jeep Liberty diesel models with the 545RFE transmission. Is a faulty speed sensor possible without triggering any associated codes? Could the issue be related to transmission cooling or internal solenoid failure? Note: The vehicle has not shown engine overheating, and no other warning lights have come on since the initial incident.