Understeer is not a problem in the Raptor once you figure out the technique... in fact, I worry more about oversteer at speed... and that's with the "boat anchor" 5.4.
What I'm going to describe is counter-intuitive... but the Raptor handling is very much like some of the off-road cars I used to race short course and dez with.
My bet is that most people are trying to power the Raptor around the corner. Lots of fun in 2wd-lock at low speed! But won't work at speed. Turn the wheel and mash the gas at speeds above 10 or 20mph and the Raptor plows straight ahead 9 times out of 10... especially in 4WD.
Instead... try this. Carry a little extra speed into the corner, steady throttle. When you want the truck to rotate, turn in and LIFT OFF THE GAS and the back end will come around. Then you get back on the gas (moderately) to stop the slide and the truck straightens up... hopefully pointing in the right direction!
Kind of an "anti-power slide" LOL The official "handling" term is that the stock Raptor has "trailing throttle oversteer" characteristics.
TRY THIS TECHNIQUE AT YOUR OWN RISK and in an area where there's nothing to hit or a cliff to drive off!
It takes some practice to master... but works well once you get the hang of it... catching the slide is actually the hardest part... very easy to let the back end step out too far and that can be hard to recover from at high speed.
A whole lot going on when you do this... have to enter the corner fast enough, but not too fast... the throttle lift needs to be synchronized with the turn in... and you need to learn when to get back on the gas and how hard... but soon it all becomes second nature.
YMMV...