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Yup, mine was a 4.3L, so the actuator was under the battery tray. My t-case switch was bad, so it wasn't sending vacuum to the actuator. For a quick fix, I cut the line running to the vacuum ball, put in a T and then fed a line to the vacuum actuator. When I didn't want 4wd, I disconnected that line and plugged the T... good ol' farm fix.

On the 2.8Ls, the vacuum actuator is on the passenger's side fender - so much easier to get to!