I have a 95E300 which has the same engine as your car (non turbo six). At high altitudes it had severe surging that decreased the lower we drove. The dealer said there was a program for this, but they would not tell me what parts they replaced. Anyhow the next time we drove up to Santa Fe the car had the same problem, so I know they either didn't fix it, or there is a second problem that causes the surging. Since we live at 350 feet above sea level the problem does not occur here. Is this a similar problem you are having, or is it happening all the time?
Steve