grinding noise from rear end and other issues

hey im matt. this is my first post here. i have a 2003 tacoma with a 2rz motor. my first issue is that im hearing a grinding noise coming from the rear end when im driving in 5th gear at low rpms. my second issue is that i recently changes my spark plugs and when i pulled the coil packs, the one from the cylinder furthest back looked rusty and oily. the truck doesnt really have the power that i feel it should and i feel like these issues are contributing to it. i also just turned 214,000 miles. any idea what could be wrong?

 

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