I sent my truck to the shop to figure out why I had rough shifting with the 1st gear shift shifting the whole truck and then sluggish shifts in the subsequent higher gears and they discovered that my tcm was bad and replaced it. I picked it up and drove it blowing the tcm within 15 minutes sent it back they replaced the tcm again and test drove it. A day later when merging onto the highway to get up to speed, it blew again when I saw my speedometer flicking down which is the main indicator I've used to determine if the tcm went bad. And the bad shifting was back. I'm convinced its a faulty wire or ground but would like to get a second opinion to see if I can't just fix myself and where to start when finding a solution. 

Symptoms to note - Sluggish shifting with first gear chucking the whole vehicle. Speedometer flicking down. Left turn signal warns me I left it on too long after just turning it on. 

2009 GMC Sierra 1500 SLE Z71 5.3 V8