TPS is a possibility, it shouldn't be doing anything much at those revs with the throttle open, but if there's a knackered spot on the resistive track it could be the problem. As could a dodgy connection/frayed wire anywhere in the ignition system.
But, as you suggest, the carbs are the most likely cause.Rather than cleaning them, I'd ditch the carbs. I never get more than 85,000 out of a set before they start getting rough because the teflon coating on the slides is worn. A set of barely used ones (i.e. 40,000 miles or less) can be had for about £80.