There's a good chance that you can buy the original AC Delco (Delphi) camshaft position sensor online for a whole lot cheaper than somewhere local.
The following links will help you comparison shop for the factory original AC Delco (and aftermarket) camshaft position sensor:
Unsure if the above camshaft position sensor fits your particular vehicle? Don't worry... once you get to the site, they'll make sure it is by asking you the specifics of your vehicle. If the above don't fit, they'll find you the right one.
I've written several 3.1L and 3.4L troubleshooting articles that may be of interest to you. You can access all of them in this index: GM 3.1L, 3.4L Index of Articles.
Here's a sample of the diagnostic test tutorials you'll find in the index:
“I went to a bookstore and asked the saleswoman, ‘Where’s the self-help section?’
She said if she told me, it would defeat the purpose.”