[Tink]

The vacuum actuator is a common problem on these trucks. Is this a 2.8L? If so, the vacuum actuator is easy to get too... One way to check it, is to feed direct vacuum to it from the vacuum ball (I've put a T in the line to feed mine before). If the front axle engages, then the vacuum actuator is fine the issue is the t-case switch. If the front axle does not engage then either te vacuum actator is bad or the cable to the front axle is siezed.