88 GMC Suburban Auto Trans Problems

My 88 Suburban with Automatic Transmission will shift from Park to Reverse to Neutral to Overdrive to Drive to 2nd, but will not make it to first on the column. Reverse works fine. When I put it in Overdrive/Drive, the truck runs, but the gears will not change. It's like it is stuck in a high gear. If I am driving and shift from Drive down to 2nd, I can feel the gears change, but going from 2nd back up to drive I can not feel a change. That is why I thought it might be stuck in a higher gear than 2nd. I have checked my transmission fluid and it is fine. The transmission was rebuilt 2 years ago, so I think that is fine. Please send any suggestions or thoughts.