Could be a number of issues that are causing your shifting problem(s). Without any other information provided (like whether it's an A4LD), I recommend the basics first.
1. Check the condition of the trans fluid. It should be a pinkish color and at the appropriate level when warm. If not, then change the fluid and filter. But if your not sure when the fluid and filter was last changed I would do this regardless of the condition of the fluid. Low or poor quality fluid can cause the shifting issue you described.
1. I would find and follow the vacuum line that runs from the transmission modulator to the vacuum tree under the hood. A common problem is that the line is either cracked somewhere from age or is disconnected from the vacuum tree. Check to see if you have transmission fluid near the vacuum line or the vacuum tree. This could indicate that vacuum modulator has gone south.
2. I would check the linkage. Have someone slowly move the shift lever through the gears from forward to reverse while you observe the movement of the linkage under the vehicle. No need to have vehicle running.
3. I would change the transmission modulator if you don't know when the last time it has been changed. Purchase the non-adjustable type modulator as these are a bit cheaper and will work quite well. Search this site on how to do this procedure. Pay attention to the "pin" that is referenced in the how to guide. It's easily lost and harder to find. Ask me how I know this...lol
4. Again, if you don't know the last time the bands have been adjusted, I would adjust the bands. It's not a difficult procedure and can be done without out help. Search this site for adjusting bands and you will find some really good write ups.
If you have done all of the above and the issue still persists, it might be time for a full or partial rebuild. Depending on your mechanical ability, I might recommend that you have a qualified transmission mechanic do the rebuild.
Hope this helps. Let us know how you make out.
Willy
