I drove my sister 03 4X4 dually today because she had a predator chip put in. It felt alot faster but the throttle seems to stay at the same rpm when shifting.
kinda weird.

 

If it's a manual trans truck, you're going to notice a trait inherent in all pressure-type performance boxes.

The box commands extra fuel pressure in the fuel rail. When you let off the throttle, it takes a second for that pressure to bleed off and allow the engine rpm to come down. It takes some time to learn to drive around it. Just let off the throttle a bit before pushing in the clutch to shift.

If it's an auto truck, perhaps the trans is not liking the engine's new-found power?