1996 Dodge Grand Caravan 3.8L P0731 Transmission Code: Fix Without Professional Help

Hello everyone, My son-in-law recently bought a 1996 Dodge Grand Caravan LE with a 3.8L V6 engine, which has been largely unused and is now being used to transport my 2.5-year-old grandson and newborn granddaughter (born just four days ago). As a military veteran with limited mobility due to injury, I can only assist so much—my daughter and son-in-law are hardworking but financially strained, especially since my daughter is currently on unpaid maternity leave. Money is very tight, so we cannot afford a mechanic visit or even a diagnostic check that costs $100 in Las Vegas. The van initially showed an ABS light warning, high RPMs, and no gear shifting while driving—no engine light was present. After connecting an OBD-II scanner, we found fault codes P1784, P0715, and P-0731. We also noticed the parking brake pedal appears stuck and does not respond when pressed. We replaced both the input and output transmission speed sensors, checked and topped off the transmission fluid (which looked clean and not burnt), and cleared all codes. However, during our test drive today, the P0731 code reappeared immediately, and the vehicle remains in limp-home mode with no shifting and high RPMs. Given my financial constraints and limited access to professional help, I’m wondering if there’s a simple fix or part we can try replacing ourselves—without needing to pay for a mechanic. Any advice on what else might be causing this issue? Thank you in advance for your support. Best regards, Sandman