Tach and Speedo intermitten

[WorkinMan]

OK, so I have a 1999 Chevy K2500 Crew Cab, 5.7l & 4l80e. While driving down the road the other day, both the tachometer and the speedometer just stopped working and pegged at 0. At the same time I noticed that the transmission would no longer shift out of 1st. I am assuming that this was due to the fact that it was most likely in first gear at the time (due to my low speeds) and there was no information from the tach or speedometer to tell the computer when it was time to shift. I pulled over and shut the truck off to attempt to troubleshoot. First I looked at the gauge fuse, but quickly ruled it out when I remembered that all of my other gauges were still working properly, and it was fine. I checked all the other fuses and decided to see if I could find a loose wire while it was running. I fired it up and behold they worked again. I had been unable to get it to reoccur, until today. Again, both the tach and speedo went out (this time I watched them both drop and them come right back). Yet again the truck wouldn't shift, even after I got the gauges back, and it was stuck in 2nd gear this time (again assuming this was due to it being the last gear it was in). So I'm guessing I should probably start with check the wiring, but don't know where to start - the connectors on the gauge cluster or at the computer....? What do y'all think.

 

[WorkinMan]

Just an update on this for anyone with the same sort of issues. I found a TSB for the issue and it turned out to be the Ignition Switch. I was losing power to the transmission computer resulting in the loss of the gauges and default of 2nd gear. I had to carry around a test light with me and whenever it started acting up I was able to pull over and test the fuse for transmission and found that it had no power with the truck running. Hope this can help someone in the future.