Also, please help people out by giving a descriptive thread title. Cucv can mean anything but something like "need help batteries draining on cucv", or " cucv electrical problems battery draining". Descriptive threads will help. Most people do not read everythread so some that could have helped may skip this one not knowing what the thread was about.
First, Check the batteries to make sure they are good.
Next connect a light between the ground and the negative terminal with the negative terminal disconnected on the front battery. If the light glows you have a drain. Start pulling fuses until the light goes out. When the light does go out you know you have found the drain in that circuit.
If one of the alts are bad they may still charge but will drain the battery when the engine is not running. Also, are both batteries draining or just one draining? This can also tell you something. The rear battery supplies the 24 volts and should only be used during startup except for running the volt gauge or any military radios. The front battery does the rest of the work for all the 12 volt stuff on the truck.