I'm told overfilling a transmission can make it over pressurize and create leaks through the seals. Beyond that I can't relate. The transmission on my 96 GC was leaking for about 3 years. I would just check the level weekly and top it off. I was adding a quart every 3 weeks after 3 years so I spent $700 at a local shop to fix it. They had to remove the transmission and change seals. Fluid was leaking past the forward pump seal then out a sensor on top of the case where it would collect and overflow creating a puddle or shoot back and coat the back hatch. The hatch didn't turn red. It made it sticky enough for all the dirt in the world to stick to it. Please let us in on the fix.