Bloody hell smogbob! Your post could almost have been written by me, verbatim. Although I'm the (relatively) tender age of 52, my knees are shot, back knackered and now my right elbow is seizing up too. Gradually losing the strength and control in my throttle hand as a result (thank Christ I'm left handed, so I won't have to give up
everything 

).
The RT was supposed to be my last big bike before consigning the garage to sub 500s, but I'd wanted/needed another GS for years, so here we are. If I can find that same perfection place you're currently at - and often the journey there is as rewarding as the destination - then I'll be a happy old tosser.
Cheers gents. In fact, I've got the original pipe hidden away in shame corner, in the garage. It's in really sh1t order, mainly as a result of my own stupidity, but it's only aesthetically fubared (long story, off topic, shan't bore you with my idiot's tale) so considering it may be exacerbating the issue, I'll try it out and see if the surging stops.
But I'll do that AFTER fitting the AF-Xied units... This probably sounds like lunacy, but I don't want to cancel the order now it's in progress and if the mod fixes the bike up, well I must confess to the big difference between me and smogbob: I like a vocal exhaust pipe - but then I'm half deaf already

.
If it does come to trying my wrecked OE pipe and this turns out to be the cure, then I'll need to pay fleabay a visit!