You do not lose any power with larger tires, at least in the sense that the engine is what supplies the power and unless you make changes to it, it'll put out the same power regardless of the tire size. You may lose some effective power in that the larger tires are harder to turn (heavier and have more rolling resistance), you'll have a larger frontal area to push through the wind and if the engine has to turn at a slower RPM for a given speed, it may be operating at a less than ideal point in the torque curve.

What you do lose with larger tires is effective gearing. Going from 28->33" tires is a change of about 17% in the effective gear ratio. This means you engine has to work 17% harder in a given gear with the taller tires. You can always shift to a lower gear. Since 4th and 5th gears are about that same ratio apart, if you drive in 4th with 33s, it would be the same as 5th gear w/ 28s. As long as you have a lower gear to use when needed, you can compensate for the tire size. And you have low range in the t-case for off-road use. Sand and mud generally uses high wheel speeds than you would use in rocks, so may not be a big drawback. If you find it is a dog, then re-gear.