It shows error code P1000, what is the problem and how to fix it?

That code simply means battery power has been disrupted to the onboard computer (ECM) by unhooking the battery cable(s) or memory has been reset by a scan tool or code reader.. Ignore P1000 code until truck has been driven enough to complete the drive cycle... That code was in the computers memory when the truck first pulled off the assembly line, brand new, until it was driven to complete it's very first drive cycle !