If it is a 3 speed auto it is quite unusual for `93 and must be a C6. There ia an adjustment for the band but I can`t remember the exact proceedure. If you do a search here you should get it.
However the problem you describe would, I feel, more likely be a vacuum problem. If you look at the trans you should see a vacuum pipe coming off the frame rail to a vacuum modulator on the trans. Pull the pipe off and look to see if there is any trans fluid in it. If there is then replace the modulator. If not check that there is vacuum at the pipe with the engine at idle. Hope this helps.