I've read almost all of the posts here about jumping tachometers trying to answer my own question. I've had the truck for a year now. I just had the transmission rebuilt and new flipl and speed sensors installed. The other day I was driving down the road and my tach started jumping around. The only thing I changed where the tires. I went from 235's to 285's. I wouldn't think that would cause the issue. I tested and installed a new tach sensor but it didn't fix the problem. I also checked the TCM connection and all is good. When it does act up the OD light does not come on. I am also having an issue with the temp gauge too. I changed both sending units and it will jump around some times too. I'm wondering if I don't have a bad ground or a short causing my problem. What do you guys think?

 

sounds like you have a bad ground in the dash cluster.

 

I've pulled the cluster out and took it apart. I cleaned all of the connections and checked the dash ground. I even changed out the tachometer with a different one. I checked and cleaned the connections from the tach sensor to the wiring on the pass side of the truck. It's still acting up. Anyone have any other ideas?

 

I've pulled the cluster out and took it apart. I cleaned all of the connections and checked the dash ground. I even changed out the tachometer with a different one. I checked and cleaned the connections from the tach sensor to the wiring on the pass side of the truck. It's still acting up. Anyone have any other ideas?

 

So, I've spent all afternoon working on my truck. I swapped out the TCM with a re-manufactured one. I swapped out the voltage regulator. I pulled the cluster out again and checked and cased all the grounds. I even bypassed the tach sensor wiring harness and tapped back in just before the TCM. I'm still having issues. when I was driving home it would normally act up around 60ish. it would rev up from 3000 rpm to around 3500 rpm then drop to zero and back up again. almost like I'm stomping on the fuel to get down the road but I'm not. at no time did the OD light flash. I'm at a loss. I'm sure there is something I'm not seeing or overlooking.

 

Anyone have any input?

 

Can't remember where the post was, but it described how to remove the instrument cluster to dis-assemble the tach gauge. The object was to clean the brownish residue off of the back of the pc board withe some cotton swabs and alcohol. I did this when my tach was jumping and falling. Fixed the problem !