tachometer jumping around

[brad k]

has anyone else had any trouble with their tack jumping. mine '06 has been going from 2200 at hwy speed to 3200 and back quite often, it is an intermediate problem and hate to take it to a dealer and have them say there is nothing wrong. it doesn't seem to effect the performace of the engine even when it jumps to redline. it has the g56 transmission so there would be none of the auto upshifting or downshifting, just drives me crazy to see it redlined when it isn't. help