The weight diff is around 30 lbs, which is offset by any aftermarket k-member. Staying 2V, horsepower will be similar (obviuously 5.4 will have more but not too much more) but the torque is sickening. Mileage wise, I'm assuming city is a tad worse but from what I hear, highway is similar. As far as the trans, the stock T45/TR3650 will hold up fine, if you drive like a granny. As for the Lightning engine, don't expect the blower to fit under the hood but if you use the shortblock, beef it up w/ forged internals. Check out the link I posted since any question you will ever have is probably answer there.