Ended up uploading the most recent USPS_default extension and calling the USPS on the telephone. The person I spoke to changed my settings and it now works...but only for USPS Priority Mail--not First Class parcels. Decided to offer Flat Rate shipping also, and will ship First Class when people make that selection. (I sell tee shirts, so they don't weight much!)
I did upgrades through version 1.9 (manually) but the admin screen still shows I'm running Ver. 1.5. Since the website seems to be running fine--and the USPS extension now works--I am not attempting further updates.
