Did you stand on it?
Did you try manually selecting 2nd?
---------------------------------------
When it shifted out of first and started slowing I gave more and more throttle trying to get it to accelerate or at least hold speed. Once it was floored it finally dropped back to 1st but was over 5k RPM. It would accelerate quickly then, so it wasn't long before it dropped back into 2nd which started the same problem again.
When I manually shifted the gear selector it showed that it was in 2nd. I manually shifted it to hold first gear where it had plenty of power to pull and accelerate but I was stuck holding that gear at 25mph and 5k+ rpm to the top of the hill.