Having to Shift Manually with Automatic Transmission. Help!

Hello,

Well. Here is the deal. My mother is now a new owner of a 1998 Chevy Blazer LS 4x4 with 156k 4.3. The problem she is having is that, when driving. She has to shift through the gears manually on an Automatic Transmisson. When she puts the truck in (D) Drive. It goes nowhere. In order for it to go anywhere. She has to shift up through the gears from 1st-2nd-3rd and then Drive. What could be the problem? She bought the vehicle at a local auction and did not realize the problem until after paying for it and going out to take it home. On her way out the seller comes out and says he forgot to mention it on the auction block. Since she bought it as-is, she cant return it. So any help that you can provide would be great.