gohan isn't a full blooded saiyan like goku and vegeta. he doesn't think about fighting 24/7 like they do.
if gohan had the killer drive that they did he would surpass them easily. look at what he was able to accomplish before he was even a teenager.
Trunk did . He isn't a full blooded but he's staying tranning.
Gohan wasn't built like that in the beginning, He was crying and bytching too much. If it wasn't for Piccolo taught him how to be a man and Gohan wouldn't be shyt.