there’s what the law says and means to anyone who understands plain english, and there’s how lawyers and the courts read and apply that language. The two are not the same. if you were ever in the Army, you’re familiar withe adage:
There’s the right way to do it, the wrong way to do it, and the Army way.
It’s kind of like that.
You can claim all you want that the law requires proof, but, to enforce the law, you have to be denied and go to court, so essentially, you have to prove to the court that the modification is incidental or not related, rather than what the law actually says.
As
@FordTechOne opined, a lot of this equation is done at the dealer service advisor level, sometimes without the input of the mechanics, sometimes with. He’s right above though - and I agreed above if you altered the ride height, I think Ford wins that case. They’ll certainly claim added stress on the diff, put up 1 or 2 expert witnesses they keep available for their staff lawyers and it will be difficult for you to disprove. Not impossible for sure, but if you lose, you lose lawyer fees, expert witness fees and you still need to repair the truck.
whomever “hears” the presentation of the facts, typically a jury, will not be experts in all likelihood, and the topic matter will be well over their heads which puts this into the realm of who is more likable, popular and believable, in that order.
I don’t personally believe what you’ve described caused the failure but I’m also not a powertrain engineer tasked with evaluating drive train issues.