Yep, I’ve spent a nice amount of time and money changing fluids...Have you tried changing the fluid in your transmission, transfer case or differentials yet? Might see if that doesn't help.
Also, I don't know if it will help the grinding, but if you aren't tuned already, you should really look into it. It will get rid of the clunky, hard shifts. And tuners can account for your bigger tires. If I were to recommend someone, it would be Jason Hackler's tunes (hACKman customs). Can be got directly from him, or through Shield & Spear Performance who sell his tunes. I'm very happy with my truck after the ECM and TCM tunes. The driveability and confidence while driving is improved drastically.
I’m reluctant to try any tunes because we live in communist California and would hate to flunk a smog test... not to mention warranty concerns..