Welcome aboard The Trophy. I don't have an AWD so I don't have much info for you. As far as tire sizes for 20" wheels, 255/45/20 is the stock tire size for the SRT so you might find a few more options out there. Check out tires-easy.com for some of the best tire prices around.
BigBob has an AWD - hopefully he can point you in the right direction regarding suspension work (fwiw, he's running the UAS air-ride kit).
Again, welcome to the forum. Make sure you go here and tell us a little more about yourself and your ride:
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