[Cliff R]

Adjustable modulators will provide the tuner with a small range of adjustment and it will for the most part only effect light part throttle operation. With heavy and full throttle the vacuum falls off enough that the modulator no longer becomes a player, very similar to a distributor vacuum advance.

Most will provide an adjustment range of about 3-5 mph from one end to the other. Make very small adjustments and drive the vehicle after each one till you get it dialed in where you want it......Cliff

[Formulajones]

I usually have to make 1 full turn at a time to see any real change.

Elevation has a huge affect on them as well. Up here at 5,000 ft I had it adjusted for nice part throttle shifts. But when I drive it down to sea level the darn thing would get into 3rd gear before I hit 20 mph.

So I basically had to adjust mine for somewhat longer part throttle up shifts at 5,000 ft. so the car would shift more normal when down at sea level. And you'll notice the change as well. Car shifts harder and holds shifts longer up on the mountain, but down in Phoenix the shifts soften a bit and are at normal shift points.