I have a '98 A6 wagon, 111,000 miles and very well maintained that generally shifts just fine. The only problem is when I am driving up a canyon, or up a long grade. The car upshifts just fine (either to 3rd or 2nd, depending on my speed), but when the road levels back out the car does not immediately shift back into 4th (or 3rd as the case may be). It may be as long as 10 to 15 seconds before it downshifts. This only happens on longer hills. I just fully serviced the transmision, but the problem seems to be the same. Any suggestions? Thanks in advance.

I have a '98 A6 wagon, 111,000 miles and very well maintained that generally shifts just fine. The only problem is when I am driving up a canyon, or up a long grade. The car upshifts just fine (either to 3rd or 2nd, depending on my speed), but when the road levels back out the car does not immediately shift back into 4th (or 3rd as the case may be). It may be as long as 10 to 15 seconds before it downshifts. This only happens on longer hills. I just fully serviced the transmision, but the problem seems to be the same. Any suggestions? Thanks in advance.

Try letting off of the gas. Make sure the car is warmed up, and that the road is actually level. The transmission has a grade sensor that senses whether or not to hold the gear if you are climbing a hill.
Also, make sure you drain and fill your transmission fluid and change your filter.