Is or was this a rebuilt transmission? And how many miles on it since it was rebuilt?
Is it starting out in second even if you manually move the shifter to low?
I would look very close at the governor valve being stuck in the bore of the governor. Transmission shop can do that very easily and quickly. Or you can too. I think I sent you a pm on how to check it.
Once at a stop, if you manually put the transmission in low, does it start out in low? If so, I think the governor is going to be the first thing you should look at. I bet the valve is stuck.
Good luck and let us know what you find.
