Agree with SRMMMM, even if the T/conv is the problem, it will dump a load of rubbish in to the trans... At over 150k refreshing the trans is not a bad idea.

I did mine for under 2k all-in but that was in my garage. Not a shop charging 200/hr. I've got almost 50k since my rebuild, so it was worth the pennies.

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2003 4.4i black ext./black int./black headliner (kid's runabout)
2014 535d X-drive, M package, silver/black interior

Sold but not forgotten:
2009 E70 35d, black ext./black int./black headliner (sold 2021)
2006 4.8iS Le Mans blue/cream int./black headliner, SOLD in 2012 sadly...

Other hardware:
2015 Cayenne S (wife's new DD and definitely wroooommmmm)
2016 Tundra 1794 edition crew cab, luxo hauler
2005 Tundra crew cab, weekend hauler. Sold after 150k very happy miles.