Normally I can get 6-8 times, the last couple times the locks are really slow. Was your ACC turned off? I think if anything is on when you shut the car down it closes some of the flaps and you lose some vacuum there.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k