I cant get my truck out of 4 wheel drive

i cant get my truck out of 4 wheel drive.it has the automatic push button for 4 wheel high and 2wheel low.it should come out of 4 wheel on the fly if i depress the 4 wheel button again but it dont.it does shift from 4 wheel low to 4 wheel high in neutral. i have replaced 2 vacuum lines that run from the actuator under the battery and one to the main vac i think ,they where dry rotted pretty bad.i also replaced the vacuum switch on the transfer case,i took it out and the ball at the end did not move at all (the new one did) , so it need to be replace too i guess.i changed the fluid in the transfer case and screened for shavings...none found.is there a common thing that wont allow it to engage and disengage, that i can check?is there a manual way to disengage it at the transfer case?im going to look at the thing i believe to be the actuator thats under the battery tomorrow.can some one tell me what to look for in a good or bad actuator or any other thoughts.thank you for your time.