Are both tires the same brand and type? Are the shocks in good condition, 05 is getting old. Have you checked the rear swing arm bearings and their preload setting? Use the stock tire pressure of 36 psi. front and 42 rear.
Not all brands of tires work on every bike. You can put the bike up on the center stand and grab the tire at 3 and 9 o'clock. Try to wiggle it. It can move in 3 locations, the final drive right in front of you, the final drive pivot point where the drive is attached to the rear swing arm and the rear swing arm up forward where the rear shock is attached. If you do not own a Clymer's book on the bike get on. Checking that the preload on this swing arm pivot is correct is a good start. Read how to open it up and grease the bearings then reset the torque on each side to the specific settings. It is complicated. Requires a 30mm deep socket and torque wrenches.
Lots of things contribute to tank slappers and this bike is not naturally predisposed to them. One is holding on too firmly. I am a firm believer of changing both tires at the same time. Following the one at a time plan leads to trying to get the most miles out of a tire and using it to way past it's prime. You can expect about 4500 miles or less out of tires on this bike.
Others with more specific information will chip in I hope.
There is what is called a "deflection lever" that helps tie the bottom of the rear shock to the rear swing arm. It has two needle bearings and the rest of the system has two more. They need to be opened up and serviced (cleaned and greased) every two years. They can bind and actually break this lever, sometimes referred to as the bow tie. At one point there was a recall to install a stronger one and point out the need for this two year service.
Here is an article with some good info. I like the comment about front wheel bearings. An easy one to check, remove the wheel, stick your finger in the bearing and turn it, should be smooth and turn fairly easy. This is a good time to grease the lip seals before re installing. The tire guy may not have.