Out of curiosity, what type of truck does he have? 2500, 3500... 4x... 2x... . auto... stick. . ??
I ask because when we had our dyno days here in Colorado we were playing with EZ boxes and we noticed that the EZ gives more power to a truck with an Auto transmission then one with a Manual transmission.
We had several instances where we noticed that an EZ will only give a truck with a manual transmission around 10HP (I dunno if it's an altitude thing or what), though trucks with an Auto transmission were seeing anywhere from 20-30hp gains.
Hope this helps
Kev