I am running 295/70/17s at 65 psi. It feels like I am riding on bolders, I can feel every little bump like Im hittin a pothole. Sometimes when I hit a good enough bump the whole back-end shifts. My question is , I know I can go down on the psi but how much without abnormal treadwear. If anyone else has this setup or has some "know-how" Id appreciate some insight. Thanks in advance.

 

Not enough information. Are they load range C, D, or E. As a guess, as you are running at 65, which is usually the max for a load range D, use about 45. The number on the tire is the max for the tire, not what they should be inflated too.
If it is a load range E with a max of 65, 45 or a little above will be about right. Also if the tire replacement is the same load range as what came on the vehicle originally, you can use the sticker number. If a different load range, don't use the sticker.