Ok, let's review...
Check your tire pressure again, something like 18/26 should be a good start.
Set you're rear shocks softer, not harder. One notch down from the middle would be a good spot to start.
Loosen the front axle, axle pinch bolt, and lower triple pinch bolts, bouncy-bouncy-bouncy, tighten the triple, tighten the axle.
Make sure your rear wheel is properly aligned.
Make sure you don't have excessive play in the steering head bearnings (you probably don't or you'd notice it sooner).
Scott - This was very helpful review. My G5 handlebar and overall bike vibrations had become so bad that it was very uncomfortable above 50 mph. The forearms and elbows would become numb, very uncomfortable - on the verge of pain - due to constant shaking, as if attached to a vibrator. I even bought foam grips that slide on top of the OEM handlebar ends. Obviously the problem was still there because they were not going to fix the real problem !
After I read your post, I thought why not try it - the bike is in bad shape anyway. So, I took off the windeshield. Loosened pinch bolt of front axle, loosened front wheel axle nut, loosened pinch bolts of each fork - G5 has a brace between upper forks attached by the pinch bolts. Put the bike on center stand, ran engine at idle with a couple of blips of throttle and then let it idle. Keep the handlebar front wheel straight. Went round and round tightening the fork pinch bolts, then axle nut and finally pinch bolt of front axle - got that really tight.
Set the front tyre air pressure at 19 psi and rear at 27 psi. Rear shocks all the way down, at the soft setting.
Went for a ride - What a significant difference it made, as if I got my bike back. The vibrations were of much shorter duration and more like mini-vibrations. Took bike to 70 mph but the wind was too much to go any faster so came back
!
I am going to put back the windshield and then test it again to see if windshield helps or makes it worse.
Beer to you from my side
!