3rd gear bog over rough terrain

There is an uphill trail at our local riding area that is covered in whoop-like bumps. Maybe between 1' and 2' in height, varying lengths. When I hit them in 3rd gear, holding it wide, probably about 3/4 of the total revs, I get bogging from an otherwise perfect running motor. My bike is bone stock with the exception of an FMF programmer to richen things up a bit. It seems like the motor is starving momentarily, then picks right back up. Fuel sloshing around? Bad fuel pump? (it is an early model 08') Other ideas?

First guess:

https://wr250rforum.forumotion.com/t7636-cutting-out

for what its worth i keep my wrr factory standard i have a problem free bike it does what i want off and on road yamaha know what there doing when they develop a bike if i wanted more power i would get a bike with more power I'm a believer of not messing with things all the add ons you can get to make a bike faster is somewhere along the line going to upset things try going back to standard and see if the problem is still there

First thing I'd do is check battery terminals and make sure they're not loose.

Then -

If everything is stock, except fuel programmer, I'd remove fuel programmer and see if problem goes away.