my gearbox slips or shudders when I start to accelerate thru the low gears.

I assume it's a manual transmission, more then likely clutch disc or weak pressure plate. higher speeds is not using the same amount of torque.

AGREE WITH #1. HOW MANY MILES ON THIS CLUTCH?

What ended up being the problem? What did you u do to get it fixed? Cost? My 2007 BMW X5 4.8i E70 is having identical problems. As long as im on highway and being easy on the gas it usually dosent have problems. But when I have to go up an incline seems the gears have a super hard time shifting in low gears. X5 will jerk and the shifter will make clicking noises. 4x4 brake dsc lights come on of course. If i let it sit for a little then restart i can make it home. Sometimes i have to oull over and let car sit 3 or 4 times though. 84000 miles. Should i change transmission fluid? I dont have enough money to pay bmw 185 to run a test right now plus repairs. Any advice would be appreciated. Thanks. Jeff from Denver COLORADO