I am not sure why you guys have such a hard time believing the problem is the fender...
I'm not trying to be a smartass. I've been riding since "Wobble and Weave" was a newish film. The KLR has been my bike of choice for the past 10 or 11 years. I have ridden it, in completely stock form and in a completely 'transformed' form with the stock fender at 90ish mph for hours on end. I know the before and after* characteristics of the suspension, and I know the effects of where I put the weight, what tires I run, and what pressures I run in those tires. Truth be told, I swapped out the OEM front fender because it was unattractive, not because of instability. With good suspension, weight distribution, tires, and pressures, my bike practically steers itself in heavy winds, especially crosswinds. It's like a good horse where you just give it its nose and let it run. It's just a case of 'been there, done that, got the T-shirt'.
Neither Dave nor I are trying to be argumentative, honest. And I, for one, have no issue with someone swapping out a fender to solve an instability problem. If it gets the job done, all well and good.
Over the years I have found that the root cause of instability usually lies in not enough weight forward, crap front wheel damping such that the front wheel undulates in its pressure on the road, in the case of the tall, skinny, 90/90-21, not enough pressure causing too much deformation, and tires that just don't track for beans sometimes.
My brush guards are HDB - Highway Dirt Bike. https://www.highwaydirtbikes.com/ind...ow&ref=HDB-100
*My suspension consists of a Cogent shock built to accommodate my size and riding style, including a 1" lift, Gen 1 linkage for a bit more lift and travel, uprated springs in the front, preload adjusters for fine tuning the front springs, and RaceTech emulators. Weight distribution has included a Molle tank cover to move a fair amount of weight forward, carrying heavy things low and forward in hard cases. Tires are almost always Kenda K761 with the front mounted backward with inflation at 36psi F/34 psi R.