If the transmission overheats, it will burn the fluid. Fluid will turn brown and smell burnt if it was over heated. In extreme cases, it is possible to get so hot that the clutches start to slip and burn as a result. Change the fluid and see if it resolves the problem. The fact that it started to work after cooling off at the side of the road for a while might indicate that the transmission was overheated.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record