If I'm doing the math correctly a 0.72 OD output coupled with a 3.90 gear ratio leaves you with an effective final drive ratio of 2.808. It's a really significant change in engine rpm from the straight 3.90 gear with 4th (1.0) output with the T5, to 2.808 in 5th (0.72) output. That's really in the highway driving range and the 5th gear won't really hit the 235/261 power band sweet spot in city/non-highway driving.
You'll be fine in the lower 4 gears for in city driving with the 3.90 and this T5 though.
A note on making this change - be sure you are giving your other systems of your truck like brakes and steering a thorough going through and refresh or upgrade. Getting things rolling at higher speeds mean you have to be sure your can safely steer/stop as well, for the benefit of yourself and others on the road.
