[David]

It doesn't seem to me that there's an objective answer to this question. It all depends upon how much you value power over gas mileage (or vice-versa), how quickly you need to get up to speed, what you're trying to do, etc. My old YJ used to have a light that came on telling me when to upshift; I don't know if the TJs do or not. It seems a bit silly to me. You should feel when to shift, not rely on an instrument panel. Just off hand, for an I-6, I'd think the shift points would be anywhere between 2.5Gs for economy up to 4+ for power. Having said that, I haven't driven one in forever, and I don't pay attention to the tach. You know when to shift by listening and feeling.