Thank you all for the replies and suggestions! Replaced the front bank o2 sensors and was able to clear those codes. Waiting on the thermostat to be delivered tomorrow and another “fun filled” weekend under the hood! My hope is that this can be resolved without a tranny rebuild and plan to post a spreadsheet of parts, where they were purchased and price to hopefully pay it forward for others with similar issues. Will update with my progress after the weekend and look forward to her running as she should so I can move on to the FUN of upgrades rather than repairs!

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2002 X5 4.6is Black Sapphire Metallic/Black