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A multi-system electrical failure is almost always grounding issues. Check your ground straps.http://forum.73-87chevytrucks.com/smforum/index.php/topic,26163.0.html
rich how can putting a truck in gear and causing problems be a ground issue? not questioning your suggestion but curious. the only thing that i can think of that gets power by the shifter is the nss, but then how does that feed back to the dash?
The cab "might" be finding an alternate ground path through the shift linkage.