Engine revs rise at odd times - gearbox?
 

Driving my 2003 E53 Auto, once in a while the engine revs rise a few hundred rpm before settling back down. This happens only when I'm going uphill and I've listened in closely as I at first thought it sounded like it was changing gear but I notice it is actually staying in the same gear. It's like I've just blipped the throttle but I haven't.
Everything runs OK but I'm nervous about it being the symptom of gearbox issues.
I've had the car for 12 years and it's only started happening in the last few months.
Any help appreciated.

Check and test MAF sensor

So the engine revs higher while the vehicle is in motion going up hill but there is no speed increase? If so it sounds like s slippage of some kind. What kind of maintenance have you performed on the X5 in the 12 years that you have had it? By the way is your X a 6 cylinder or 8 cylinder model?

Took the MAF sensor out and cleaned it with MAF sensor cleaner - no change. Not sure how to check it further without buying a new sensor.

Yes, no speed increase. It does feel like something is slipping.
The vehicle has been serviced exactly according to the requirements by my BMW dealer - all dealer serviced. In the 12 years all its had done is a fuel injector replaced and the middle fuel pump replaced. It is due an inspection 1 next month.
It is a deisel 6 cyclinder 3.0

The most common cause of a slipping transmission is low fluid. It could also be worn clutches in the transmission or the torque convertor. Does it slip in all gears or just road gears. Is it all rpms or say 3,000 or more?

I would pull the fill plug and see if a small amount of transmission fluid come out. There are two factions regarding changing transmission fluid. Do or don't do it. I change the transmission filter and fluid every 50,000 miles. If the fluid is low I would change it with the proper ZF fluid. However, the major of the times the fluid is changed because of a transmission problem it is too late to be the fix. Is there any unusual noise or vibration when it is slipping?

MAF does not cause slipping. It will cause a loss of power and rough running. The MAF is a primary contributor to air/fuel ratio.

With motor running...does your tranny hold gear when you release the brake pedal/parking brake on a slight uphill?

I suspect your experiencing some tranny issues