All Electrical Power Gone!

Got in my truck to start it the other morning and no power at all to anything. next day went out in the afternoon, hooked up jumper cables to jump but I didn't need to. It started on first turn and seemed to have full power. Let it sit a day and it starts no problem. Seems to have full power. We had some problems 3 months ago and replaced the battery and had the alternator checked and they put a gauge on and said the alternator was OK, not the best but OK. Thanks!

Poor grounds could cause issues similar to that.

The alternator itself may be ok, but the connections (wires, terminals, etc) may be screwy. Something might be loose, there may be some corrosion, a pinched or broken wire, something of that nature.
It might help to list the year, make, and model of your truck. Some vehicles are known for certain issues, maybe you have a truck that's known for electrical problems, we don't know yet.