Transmission will not shift properly

My 1987 hardbody truck is burning transmission fluid through the intake
manifold. I found that the modulator valve has been compromised and
allowing tranny fluid to be sucked into the intake manifold. When the
vacuum is low, there's no smoke. But when it's at an idle! After idling
at a stoplight for about 30 seconds, white tranny fluid smelling smoke
billows from the tailpipe. I replaced the modulator only to discover
that it will not shifr from 1st to second gear with the selector in
drive. If the selector is in D2, it will shift ONCE and stay in that
gear. Is the modulator adjustable? OR is there an adjustment that I
haven't done to get this transmission to shift correctly?