I have a Tahoe that I just purchased. It is a 97 Tahoe with a 5.7L engine and a 4L60E Transmission 4x4. I bought this vehicle due to mechanics were charging to much to repair and the owner could not afford it so I took it in my hands. This is the problem, reverse is the only gear that works. Please read carefully. The vehicle will only operate in reverse. The PCM sends the proper signals to the transmission. First, second, third no luck. There is no short in the wiring. Now if I disconnect the wire harness to the transmission the vehicle will operate now in third gear and reverse. I've read that this is known as fail safe mode. Ok the vehicle should also operate in manual second gear and it doesn't. Now keep in mind this is with the electrical harness off. The fluid levels are ok. Oil filter has been replaced and there were no metal parts in the pan but a small amount of gray mud. I've cleaned the harness plug it back in again the vehicle will only operate in reverse. I know there are a lot of threads similar to this but nothing saying the issue that I am having. I would like to know is there anything I can look at before a do a R&R?