I agree with pushrod.
maintenance is vital, but if its not broke don't fix it. the unsweet spot is common on most engines....motorcycles, boats, cars.(some are more pronounced than others) For example, I cant stand that my overdrive kicks in at 40 m.p.h. in my truck and the engine drops r.p.m. and it starts lugging until it downshifts....its a common problem that the manufacturers do to get the fuel mileage right for the e.p.a. Drivability for the customer isn't really an important factor, but government approval is. So, in my truck I manually shift out of overdrive until I hit at least 50 m.p.h. or keep my foot into the gas until then.
Some, maybe many will disagree with this statement. An engine will only run in its "perfect form." When it is at its peak of its powerband.....any other time it will be either lean or rich. (Remember your first 2 stroke dirtbike gentlemen?) The EFI systems have cleaned up this problem a lot but it has not perfected it.....yet. It is possible that if you try and resolve this low speed surge it may cause issues somewhere else in the r.p.m. range/curve. you could actually lose h.p. in the mid to upper range by "cleaning up" the low end...of course this is just my opinion. Me personally, I'm a Torque junky, a zero to 60 guy. I'm more concerned about the full throttle mid range torque area than I am with my 1st. gear surging. But if you feel you must chase it down happy hunting to ya!