The procedures for looking for a vacuum leak are identical between the two vehicles.

Start at the vacuum pump and make sure that you have over 20" there. I presume that you do, because you mentioned nothing about the brakes giving you problems.

Then proceed down the vacuum lines and look for bad hoses and/or connections. When you find a connection, hook up the gauge at this point and ensure that vacuum makes it to the connection. Then move on down the line.

If the brakes work properly, you may have a bad hose inside the vehicle that prevents the door locks from operating, however, I'm more inclined to believe that the issue is under the hood, because the transmission is flaring.

Something else seems amiss, however. When the transmission loses vacuum, it acts in just the opposite behavior of a flare. You typically get a very hard shift. Flaring occurs when the trans has too much vacuum, or, when there are worn components within the transmission, or a combination of the two scenarios.