Transmission appears to be starting off in 3rd gear from a stand-still. If you place the gear selector in 1st, the truck will start off in 1st gear. When manually shifted into 2nd, it stays in 1st. When gear selector is moved to "Drive", the transmission shifts into 3rd gear & at a correct speed into 4th. When slowing, there is no down shifting noticed. Anyone have a clue?