At least it sounds like it's not likely your trans.

Unfortunately you are no closer to a diag. There aren't that many things on the N52 that causes driveability issues but doesn't throw a code. Though your accelerator pedal code, if it is an active code, could be a pointer in the right direction. Have someone drive around while you monitor INPA or ISTA live data to see the throttle duty cycle. See if there are any anomalies.

__________________
2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)