Low voltage when engine is hot

I have a 94 silverado.  When the engine is "hot"  normally on a hot day here in PHX the battery only charges at like 10-12 volts.  When I turn the engine off and start it again it is "barely" turning over if at all.  After it sits a few minutes it will start up fine.  When its night or I make short trips the battery charges normally at 14 volts.  The battery is fairly new, I havnt upgrated the "big 3" yet but the cables are in good condition with no corrosion and gold positive terminal and connectors.  Would the heat have a affect on the alt or battery?

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Im moving to MEXICO and Im not speaking spanish!

Now it's my turn to be confused 

Engine bays are hot places, day or night, Phoenix or Ann Arbor.  That is the climate the engine and electrical system are designed to work in.  You should take your truck over to a good garage and let the mechanics have a look at her.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.