Have a strange issue with a 2005 Columbia. When splitting 6th from lo to hi occasionally the check engine light will come on and the speedometer will stop working. It's sequential, the shift completes, a second or two later the light comes on, and a second or two after that the speedometer winds back to zero and stays there until the truck is turned on and off again. Since the truck's computer has been tweaked to encourage progressive shifting this also has the effect of governing the engine at 1400 RPM. Asked the mechanic about it and he shrugged. Anyone seen any thing similar?