So it sounds like your pump is generating good vacuum, and it's not being leaked out by your malfunctioning door lock system (your check valves are still good). Almost all of my vacuum was being lost by my door lock system (my engine would not shut off) and I now have it plugged up, pending repairs.
Personally, I'd rather have manual door locks than spend the time, money, and trouble diagnosing and fixing my door lock system. I have a coupe, however, so that's easier for me to decide.
If you really want to tackle this job, however,
www.**************.com offers a manual printed specifically on the subject of troubleshooting and repairing the door lock system. I can't vouch for how good that manual is, but their others I have are probably a 7 on a 1-10 scale.
Basically, what you'll be doing is removing door panels, checking for unplugged vacuum lines, then using a mityvac (a hand pump which generates vacuum, at any autoparts store) to pump up the lock actuators and test them for movement/leakage. You'll also test the central locking actuator at the driver's door lock, the main vacuum reservoir and various other components.
Good luck if you choose to try and fix your system!