I know, the obvious thing to check is the batteries. The volt gauge says that everything is charging fine (above 14 volts) but the truck is dead. It has been sluggish starting lately too, even after it has JUST been running. Is it possible that the alternator is not charging the batteries properly? I just replaced the alternator about 2 years ago. What should I check?

 

first is it turning over and not catching or is it totaly dead?
if the starter is turning but acting like its not getting fuel, check the Fuel Shut Off selinoid wiring connector on the firewall end of the IP. They have been known to work loose.

You can try "shaking" the wiring bundle on the drivers side wheel well, there are a few connections in there that can come loose and cause it to act totally dead as well

 

My truck had a similar problem. The voltage gauge in the truck said everything was fine, 14+ volts. I figured the batteries finaly had enough. I pulled the batteries, took them to a local parts store to get new ones. While there, they checked them and verified one was incapable of holding a charge, while the other would hold about 60% of it's capacity. I put the new batteries in and a couple days later, same problem...batteries dead and couldn't even start the truck after I had just shut it off no more than 20 min earlier. The voltage gauge had been saying 14-15 volts the whole time. It would even show a voltage drop as normal when the heater in the intake would cycle just after start up. I pulled the alternator and took it to the parts store to have tested. The alternator was weak. It was not completely dead, just not putting out what it should. I replaced the alternator and haven't had a problem in the 2.5 yrs since. If I had my load meter, I probably would have picked up on the alternator earlier, but, I lent it out prior. So, if you have a load meter, use it. It might help, especially since the voltage gauge in the truck can be misleading.