Thanks for the info on the plugs.
Back to the ruff running. I guess the thing I can't get my head around is the going from the bike running perfect on the last ride, to this ruff running, backfiring and having to keep it above 2K to keep it running, the next time out. Is it more likely that a jet is clogged? Can the TPS go wacky from one day to the next?

 

Sounds like time to do an internal carb clean. You can try the easy non-stripdown way first, but I suspect you will end up doing a strip down to do the job properly with an aerosol carb cleaner and compressed air.
If you have tools and a manual and some mechanical ability it will only take a careful 2-3 hours. Note the carbs are different front to rear so do one at a time and reset the carb synchro when you are done. Be careful with the TPS, choke parts and diaphragms, they are very fragile.
Last few times for rejetting, I have left the choke assembly attached.

 

The symptom came on really fast. In the free or cheap catagory drain the float bowls and put some fresh high test in the tank. The description you gave made me think of contaminated fuel or water in the float bowls. I had that frequently on my airhead bimmer with just those symptoms.

Also in the cheap to check zone, how about the vacuum lines between the manifold and the petcock? Some vac leaks are more obvious at low rpm's.

 

I did mention that mine did the same thing. One day running fine, albeit there was always the occasional backfire/coughing thing; the next day, wouldn't even idle. I couldn't believe it either. I didn't really want to start tearing things down in the summer, but had no choice. Mine was running at 800ohms the year before and i figured leave well enough alone, then one day it happened...wouldn't idle. When I took the tank off, I thought I may as well do whatever else had been suggested, so....set air mixture at 2.25 turns out, shimmed needles .40, cut air box flap and cut filter out and put a piece of foam in on top of the screen, K&N grease around the perimeter, and their oil on the foam, and cut the rivets holding the TPS and turned it to the right until you feel the spring engage(450-500 OHMS), drilled a hole and screwed it there. There are other ways to do this that don't require drilling. Cut the rear baffles from the stock exhaust cannisters, and put everything back together and it runs better than ever. Should have synced the carbs but wasn't ready, but this winter for sure. Anyway, I'm not good with all the technical reasons, but hawkrider and others on this forum seem to know their **** relative to getting the hawk running sweet and thanks to them, it is.

There are likely other things that could cause your particular issue, which was also the case when I took the plunge, but I figured I'd do this stuff anyway and really didn't expect it to work, but to my amazement, it did.

If you don't feel comfortable doing this type of stuff, you'll need to seek help. If you were near me, I'd gladly help.