if both ecu are stock it's probably because the fuel and timing are not ideal using the p72 and when vtec kicks in it bogs down. the p75 isn't ideal either since it's not vtec and will only pull so much.

if he is using a gsr head then the p72 would be the closer match, but the displacement and timing would still need to be tuned.

the best thing to do is get the ecu socketed/chipped and have it tuned. i can take care of that for you. feel free to call me or shoot me a pm.