Game locks up if paused for longer than a couple minutes.

Nope......none of that did a thing but raise my blood pressure.

OK. Did the SP3 upgrade yesterday. That went w/o a hitch. Today I decided to build a new layout. First problem was adding bases: after adding maybe 5 or 6, I would have to wait 5 - 10 seconds before it would allow me to add a few more bases. This kept repeating: took awhile to get all 160 laid. Got that done and doorbell rang. Answered the door and then filled the dog's water and came back to game after about 5 minutes away. Game is locked: nothing works. Rest of the PC is fine: everything works. Task manager showed 1% total CPU usage.

Still having the lockup problems in Surveyor. Was at most away from PC for 4 minutes and it locked. Also now when it locks, it erases my log-in data and I have to go back and enter my user name and password. Going into task manager, there isn't anything going on: 1% CPU usage. 1.4G RAM used outta 16.

You have a major problem and then patched to SP3? That's asking for trouble because the patches are trouble especially if you have a lot of stuff added. Given you haven't had any luck solving the freezing issue on pause (don't recall anyone else having this issue), maybe you should try the helpdesk. Hope you're aware anything (routes sessions) you create in SP3 won't work in earlier versions?