I have the exact same problem with my 96 200SX SE-R, I have talked to a friend of mine at the dealer, He said he thought there is a TSB(Technical Service Bullitin) on it. I haven't yet, but the dealer should give you a copy of it if you ask
i am not sure on this, but check too see if the noise capacitor is good on the ignition system circuit. i am not positive if new Nissans use them. also, check the basics. get someone on the outside to wiggle wires and a harness and while you look inside to see if it jumps. it could be in the gauge itself.
yeah i had asked the nissan dealer to go out and take it to my car......b/c it only really happens in heavy traffic merging and the very rare case of me running it at the track......so they said they went and put it through the paces and couldnt get anything abnormal to happen......so i just installed a autometer 3 inch tach on my dash........sorta make it look a lil more serious of a car.....not just a wanna be sports coupe!!! hehe
I had the jumpy tach feature on a 1980 Fiat Brava. Turns out that the distrbutor pick up wire was starting to fray, and that was the cause, even though the car was running perfectly. That dosen't mean it applies here necessarily though. Just thought i'd through it out as an idea.