I've been battling starting issues with my cucv and I think I have the culprit figured out. Sometimes it can sit for weeks and start right up, other times only a few days.
The trucks have 2 charging systems, 2 alternators, and 2 batteries. The left alternator charges the front battery. All of the 12 volt functions run off this circuit. The right alternator charges the rear battery, which is only used for starting.
I found out that my 12 volt side wasn't charging. When I would drive after dark and use the lights I would have problems starting the next day because I didn't have 24 volts to engage the starter.
There are 2 warning lights on the dash. Gen 1 and Gen 2. They both must light up when you turn the key on to start. If they don't light up, that's an indicator that the circuit isn't charging.