This is a pretty huge grey area that I think a lot of FRF may be affected by and are blissfully ignorant.
let’s say customer a scores a great deal on a ‘certified’ preowned Rap. Customer finds a tuner hand held in the glove box when they get home and upon further research, learn that the truck has some aftermarket tune on it. Most of us are going to be like “yeah, I hit the jackpot, the work’s already been done for me”. They live contented until some time in the future... when let’s say, their, IDK, transfer case lets loose. The first thing the tech does is check for codes, 2nd thing, see if it’s been tuned. That ends the warranty claim right then and there.
BUT the owner bought with what they thought was an intact powertrain warranty. So now what?
The buyer is 100% not at fault in this scenario, the selling stealership is but that’s a difficult spot to be in and once you pony up for the repair, you will never see that full amount reimbursed on the outside chance that you actually got the stealership to admit their wrongdoing. Ford does explicitly disclaim non factory modifications right up front in their warranty paperwork when you buy the vehicle new and they keep that doc online for subsequent users, just like the owner’s manual.
OASIS lists it as a branded title with all warranty cancelled. That could also explain the problems you’re having.
So with this info, I would return the truck and get your money back at a very minimum.
That’s some really lowdown, dirty behavior right there. You should report this to Ford C/S at a minimum.