trans in limp in. code said bad solenoid pack. replaced and shifts fin at first, but after it warms up bucks from 1st to 2nd gear. now has P0740, and a catalyst efficiency code.

Hi, this is Bo, an auto expert on RepairPal's Car Genius team! It sounds like you're dealing with a tricky situation on your 2002 Chrysler Town & Country. Given that it shifts fine when cold but starts bucking once warmed up, here are a couple of areas to consider: 1. **Transmission Fluid**: Make sure you have the correct type and level of transmission fluid. Old or low fluid can cause poor shifting and might explain the bucking sensation as the transmission warms up. 2. **Output Speed Sensor**: Since you replaced the input speed sensor but not the output, this could definitely be part of the problem. A faulty output speed sensor can cause shifting issues and might be triggering that P0740 code, which relates to the torque converter clutch (TCC) system. 3. **Torque Converter**: The P0740 code often points to a torque converter issue, such as the TCC not engaging properly. This can cause the bucking you feel during shifts. 4. **Electrical Connections**: Double-check all connections related to the solenoid pack and sensors. A poor electrical connection can lead to intermittent issues, especially when the transmission warms up. Since you've already done a fair bit of work, it might be worth consulting with a professional to dive deeper, especially if the output speed sensor doesn’t resolve it. If you need any further advice or want help finding a trusted RepairPal shop in your area, please feel free to call us at 877-913-1554.