I've been watching my tyres and pressures constantly during the first season with my new GL. The TPMS has been quite useful thus far and the 10%-20% indicators seem to be right in range, and the tyres seem to be quite sensitive to weather conditions and ambient air temps (more so with the front tho). Also sensitive to frequency of riding; if I don't ride for say 10 days or so, the sensors have activated a couple times. After checking, a couple times there has been anywhere from 3-5 psi loss in pressure, or enough to trigger the 10% pressure loss indicator. In fluctuating weather and temp conditions, some pressure loss is normal (as indicated also in the manual). I now keep my tyres at 42 psi fr&rr and things appear to be just ducky. I have 5000km (3000mi) on the bike, and the wear is practically non-existant, and the pressence of cupping also nil. I experienced severe cupping on my 84 until I found the 'magic' number for pressure in the front (along with a Supebrace and Progressive springs). I haven't experienced any wobble in the steering (yet) and haven't played with the preload settings at all. So yes Boatanchor, I agree with the Detdr and say return to the dealer and see what can be warranty applicable solutions, better some compensation than none!
Since the slight increase in pressure, the harshness coming through the handlebars has also either decreased or I'm just getting used to the bike more. I could have been naturally sensitive to it after riding the ST with such a silky smooth front fork.
Sorry if I got a bit long winded with this, but just wanted to share what I've discovered over the past several months, and listening to your responses to mine and other enquiries.