I have a totally different vehicle, but did a bunch of reading on this using the search and can maybe help. On mine, the modulator valve is on the left side of the transmission, a red colored can-like thing about 1 1/2" - 2" diameter with a black soft plastic cap. There's a vacuum line from the body leading to the intake manifold. To adjust, remove cap (small screwdriver), revealing a serrated ring with a 'T' shaped metal bar lodged with each end of the 'T' in the serrations. Pull bar out, turn clockwise to increase vacuum (shift harder), counterclockwise to decrease (shift softer).

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1986 560SL
2002 Toyota Camry
1993 Lexus