2000 Sunfire Automatic Transmission Revving

How much damage was done by the leak depends on how mmuch you drove it with the level low. Yes, you would do severe damage by driving it low. Now it's full and you have problems. 2 + 2 = 4

You describe a slipping transmission and heavy wear takes place when it's slipping. You better have it looked at as the cost of repairing just goes up the longer you drive it in that condition.

I was afraid of that. I caught the leak a little late I think. I actually thought it was something else originally. Wonderful. I will do that asap. Thanks.

Classic symptom of a vacuum leak. Check closely to see if you did not disturb some vacuum line during your repairs.

What kind of prolonged issue would this cause to the engine if that is the case?

I don't see any engine issue in this case. You are not over revving the motor. This doesn't sound like a vacuum leak to me because you say the revs go up and you also feel like you are missing a gear. If the revs were going up due to vacuum you would also be experiencing acceleration, which you are not. You may not have heavy wear if the electronic control is taking the transmission out of gear when the engine revs. In other words, it may not be slipping. It might not just be in gear due to an electronic malfunction. This new problem might not be related to the leak that you had. It could be a separate coincidental failure. However, you don't say that you have any warning lights going off.

Well, the check engine light is on. I am going to stop at Autozone and see if they can tell me what it means. My dad actually mentioned the electronic idea to me, which I hope it is not. Thanks for your help Al.