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Have you checked for fault codes?
The engine light wouldn't necessarily come on if codes were stored. If you didn't find any though we can move on. How did you check for codes?
When you come to a stop and it's in a higher gear, if you move the shifter to manual first will it take off in first?
This could be a sticking 1-2 shift valve in the valve body, but it's most likely a bad governor pressure transducer. The governor transducer is a pressure sensor mounted to the valve body and it tells the engine controller how much pressure is in the governor circuit. The electronic governor is used to control upshift and downshift timing. What often happens is the governor transducer reading becomes incorrect and the controller doesn't know the actual pressure in the circuit, so pressure remains when you come to a stop, which holds the shift valves over and causes the second gear start.
The governor transducer is mounted to the right side of the valve body just to the right of the filter, easy to replace.