With your group of problems, I'd be inclined to agree on needing a trans (new/rebuilt). Will definitely be the quickest in times of turnaround. If it was just one problem with the trans you might be able to do a parts repair on yours. Or you could pick up a used trans for $500ish and roll the dice that it doesn't have the same problems your current one does.

Upallnight likes to insult the other members on the board for wanting to try to repair things by starting with cheaper fixes (even if they don't solve the issue)... but I've always thought all parts fail eventually (and these X5's are at least 12 years old now), and I have no problem using the shotgun approach if it means I can prevent a future part failure/downtime even if it doesn't fix my current problem. He gives out very good advice and knowledge, but you'll have to learn to disregard the "extraneous" material.

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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)