i wanna learn how to madify a cummins and other diesels

Okay I will take a stab at

built tranny

bigger 4 or 5 in turbo back exhaust

timing adjusted

0# fuel plate

GSK (3000 or 4000 rpm)

headwork

intake or filter

torque converter

shift kit/valve body

T-turbo upgrade

bigger injectors ( HP rating ie : X100 for 100hp injectors)