Glad to see you've made it over to here Rob. I DO know that the pre-2004 trucks had PCMs that were more limited in what you could monitor and maybe even adjust. I too, would have thought though that tire size and gear ratio would be available. The Mad Doctor (Bill) will be able to help you, I'm sure, just as soon as he gets to your post. You might want to go back and edit it to include your model year (1997) and engine info though.
That was a GOOD title you used! It should get his attention!
- Jack