97 Transmission Check Gauges Issue

Just after starting my k1500 today, the check engine light came on followed by the check gauges light. My speedo and tach died. And, my transmission was starting in 3rd gear. It stayed that way throughout
the day through 3 starts or so (I only had to drive a mile or so). Now it seems to be doing o.k. except for the check engine light is still on.
Is this an ECM problem? I really don't think it is the tranny because I had it rebuilt 50k ago by someone I trust and I have driven the truck really easy (almost no towing).
Thanks in advance for any help!

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