I'm at a loss of what to do here the pyro probe is mounted pre-turbo and I have not had it that long. It used to run 900-1000 deg. running up the hills around here and now it will not go over 800 no matter what and sometimes it just starts falling until it hits zero and it will stay there until I shut the truck off. I thought it was a ground problem but if I check all the wires they look ok I even re grounded it. Voltage problem? Probe Problem? Or is the gauge messed up? Thanks in Advance for any thoughts on this.

 

I would re-check all the connections to the pyro probe itself. The two screw connections to the yellow extension wire might be touching or shorting out somewhere that would make the gauge go to zero. I would also pull the probe out and see what the tip looks like.