I will be surprised if it doesn't get better mileage given the mileage improvements it gets in the F150 over the 3.5 EcoBoost. IMHO, the weight/HP ratio should make this happen.
I agree with your analysis that the delta between a current 2024 Ranger Lariat FX4 and the Raptor version is less than $5k which is hard to believe. How will they fit a Tremor in there, especially if you add a 2.7 EcoBoost at ~ $2,000?