Over-riding auto box to improve MPG

[Highfiddleedee]

I noticed when driving my W124 that when it changes up, the economy meter goes up also, particularly so when going up hill where the economy meter will redline as the car plods up in top gear. So, I now overide the auto on hills to save fuel. Now, most advice is to change early, government sponsered advice states that gear changes between 2000 and 3000 revs are for best fuel economy. I disagree! I think if the engine is allowed to gently attain a higher rev before changeing, say 4000 revs on hill climbes, fuel will be saved. The economy meter is I believe basically a vacuum gauge and the theory is that the greater the vacuum the more fuel will be drawn into the engine. In lower gears, the engine spins faster, the load on the engine is reduced, hence less fuel is required. So, that's how I see it, can anyone explain the low revs high gear bit, cos it doesn't make a lot of sence to me!