Yes, the vacuum modulator should probably be renamed "MAP modulator"... it increases "throttle signal" pressure as vacuum goes down (i.e. as MAP goes up)... just like the THM400/THM350, and others like the Ford C4/C6/FMX...
[throttle signal pressure assists the pressure regulator in controlling line pressure]
Various vendors make vac mod conversion kits for the 4L60E/4L80E (like TransGo ans Sonnax).
While the vac mod controls line pressure mechanically (by manifold pressure), the shift solenoids in the 4L60E/4L80E still need to be electrically driven, so a controller is still needed; various vendors make standalone controllers (like TCI).
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