ML500 - minor surging feeling: engine or transmission?

[JRHendo]

Hi all,

2002 ML500. It's done 207k kms (130k miles) mostly trouble free fun motoring here in Australia. Lately around town it's been surging a little. Always at low throttle openings. Generally between 1500 and 2000rpm in the top couple of gears. Usually under a small load i.e a gentle uphill. I'm driving along and the engine just ups and downs a little. I feel it, I think I can hear the noise changing and the rev counter moves up and down a bit -maybe no more than 100rpm.
My tech says it is showing no fault codes and maybe there is something in the transmission.

Any ideas?

Regards

John