I agree with the 'Vette Pilot. If you aren't going to use the J-Gate I would think you are at the mercy of the electronics of the transmission. Even if you find the sweet spot you are talking about how often would you be able to repeat that exact pressure on the accelerator each ad every time. Then factor in hills, traffic patterns, outside temperature over the course of a tankful of fuel and actually how repeatable would the results be tank after tank? Then factor in what you MIGHT additionally save over the course of a year with your sweet spot method and what are we talking? Maybe $50...maybe? I highly doubt you would get anything close to an additional 5mpg over and above just driving smart. I would think a tenth per gallon or so. Great you want to optimize your fuel economy, but if I am understanding what you want to do it sounds almost obsessive. I would think you would have more luck using the J-Gate and skip shifting and then getting to 5th gear as soon as possible (not even sure if you have 5th on the J-Gate as I have a manual 3.0 liter). I know in mine I skip shift almost all the time; 1st to 3rd, 3rd to 5th and can get it into 5th without chugging at about 35. I'm sure that helps with the fue economy, but that isn't necessarily why I do it. I do it mostly because it's easier to shift that way if I'm in traffic. Best advice I could give you is just be gentle when you accelerate; keep the car in perfect running order and just enjoy it for what it is and let the leaper point the way to the nearest gas station. Although you can get some decent fuel mileage for the type of car it is, it will never be an economy car.

Amen I'll sacrifice mileage for economy! I guess I'll have to experiment to see whst I come up with

Do you have cruise control?
The gearbox will change at optimum revs.
Cruise control helps you moderate your driving.
If you don't have cruise the critical factor is not the revs at which the gearbox 'will' change, but how heavy your foot is on the accellerator (gas) pedal.

Heavy use of the gas pedal so that upchanges occur at higher revs must result in higher fuel consumption.

I believe that the engine management systems are 'learning' systems... The system will adapt the engine mapping based upon your driving habits. The system can be 'unlearned' by disconnecting the battery for several hours or by pulling a fuse (same length of time) the fuse pulling is the better option as you don't have to re-enter the radio codes...
... er... I can't remember which fuse to pull (17 springs to mind but don't hold me to this), I'm sure that someone else will let us know which fuse is the one to pull.

Mike