Yes, i start moving forward but then let off the accelerator after about a second or two and then I feel the "thud". I sometimes get it around 3rd gear too when it is decelerating.

I would highly recommend that you go to your dealer and get a software update. BMW have been attending to these issues for some time, particularly with the 5 series owners.

Our transmissioons are identical (except for the torque converter) in corresponding 5 series/X5 year models.

When you drive, the driving style is 'learned' by the software and each time you move off from stop, it applies this knowledge against set values.

Measurements particularly crucial are the throttle pressure and speed of depression from stop. For economy reasons, start off is usually in 2nd gear as otherwise stop/start traffic would be horrendous.

If, on the other hand the trans detects greater pressure/speed, it selects a different set of values (gear shift points) and selects a more aggressive mode, meaning it will select 1st gear.

The four main modes are Extreme economy, Economy, Sport and Extreme Sport. Sport is selectable manually by moving the trans lever into S and XS is when you use the manual trans. There is also a Hill climb/descent mode and towing settings.

The problem seems to be in the fact that there is so many values and decisions that the computer must measure/compare that the time taken (typically 0.75 of a second) impacts on the drivers' sense of motion/driveability as a jerk/slam as you are still preessing the accelerator whilst it is thinking.

Get a software update as they have been refining these responses.

As an aside, my wife has a very heavy driving style from the lights. She just plants the foot and goes, whereas I tend to be more conservative. Consequently when she jumps into my 4.8, she scares the bejeesus out of it and I get into her 3.0 X5 and it just jumps off the line...... and scares me..

What if I get the software upgrade performed and it doesn't change? Is there a way for the dealer to determine, before hand, whether or not the software upgrade will help? By the way, I reset the transmission (accessory power for 10 sec, off 10 sec, then start) and it seemed to help with the abrupt starts at redlights, stop signs, etc. Could simply doing that help have helped my transmission, by clearing out the saved driving styles (from the previous owner)?

No, if you want to reset it completely then you have to have both the trans and vehicle ECU 'reflashed'. That allows you to let it learn only your driving style.

The only other alternative is to drive it like you stole it for a while so that you are changing the learnt values. Unfortunately, if you revert to a conservative style, the problems will come back.

It is deliberate on the part of BMW (for pure fuel economy) in it's most important market

By the way, I contacted my dealer and he said that what I did (accessory power 10 sec, off sec, then start) was reset the adaptive throttle control. That will not change the transmission but will improve tip-in response and there won't be the delay(or dead spot) in the accelerator. I drove a 2005 Mercury Mountaineer and it has the drive-by-wire like our X5s and it had the exact same issue; I'd press the accelerator, and nothing, then all of a sudden it would jerk and go, as if the drive-by-wire had some sort of delay. Therefore, I've pretty much tracked my problem down to the throttle response, and resetting it did actually help in my case, because it wasn't a transmission issue. Here's an example: when approaching the railroad track on my daily route (which is raised, so it's a little hill), I would slow down and coast over it, then resume speed once I had completely crossed it. My problem was that when I would press the accelerator to resume driving after crossing the tracks, there would be this delay before it would actually resume speed, this would be accompanied by a slight jerk. I never considered it a throttle response problem, but sense the system is drive-by-wire, it makes sense, and after completing the throttle adaptation reset process (on 10 sec, off 10 sec, then crank), the tip-in is much better, without the delay and jerk when pulling from a redlight, etc.

Excellent!!!!:thumbup::thumbup:

Jerking from stomach on cold transmission.
 

My 2009 is doing this too. But only when I start out with a cold transmission. It goes away after I drive it awhile. Mine is the x5 30I

Your rear subframe bushings are shot. Replace them and it should go away.