Support one end on jack stands, apply the brakes, release, and immediately try to turn a wheel. Ditto for the other end. It's also possible the hydro-vac (if equipped) is slow to release, so try it with the engine running as well as stopped.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!