Tachometer Jumping At Higher Speeds

In the last week or so I've noticed that when I exceed 50-60mph that my rpm's fluctuating between 1500 and 2200.. it does not seem to change the acceleration. I first noticed when I had it on cruise control running about 70mph. It's also been somewhat inconsistent, but it has NOT been observed while driving in the city.

Initially I thought maybe it was a transmission issue because it seemed like it was taking a while to switch into overdrive, but no other gears. A trusted friend with some mechanic experience drove it and didn't think it was transmission, but rather a sensor.

So... what kind of sensor might it be? What's a responsible cost to repair? What are the repercussions of not addressing the issues, if it's a sensor? Any other relevant thoughts would be appreciated.

A common problem with these gen clusters. Hairline fractures develop on the solders on the back and cause intermittant, erratic and/or non operation or all three. Maybe this is not your problem but if you have these symptoms and no mechanical problems it probably this.

Mine started as erratic then got worse. Now its intermittant at best. Mostly non operational with random bursts of erratic operation (needle winds all the way past 7k and stays there for a bit, come back to 0, et cetra)
Sometimes just as randomly it will work perfectly for a few minutes than fall back to zero, all this while driving down the road.

Bunch of how tos on youtube but so far i just havnt taken the time to take it apart yet. Doesnt bother me enough yet lol.

My 2006 tach was erratic and then finally it spun around 360 deg. and stayed under the stop peg. Cure; 1.) With vehicle off, push the trip reset button and hold. 2.) without starting, turn the key on. 3.) keep your finger on the trip reset button and watch the magic happen. Your welcome.