Put new (rebuilt) starter on last weekend, this weekend drove it for 3 hours, parked it, 4 hours later went out to go somewhere and not even a click, battery is good, headlights are on, battery cables are fine, replaced starter relay, I'm at loss, unless the solenoid on the starter is bad.

Bummer. Sometimes rebuilt starters are not actually rebuilt, but repaired. this means they fixed the issue, but did not replace bushings, brushes, etc...

try hooking up a wire to the actuater terminal of the starter (usually the small one at 2 o'clock position) and connect test light to it an ground the test light. Run this wire inside the cab so you can see it...When you turn to start, this light should light. Run vehicle until problem happens again and if the light illuminates, the focus is the starter, if it does not, you need to look at the entire circuit. Look carefully at neutral safety switch and connections..

Try tapping on the starter with a plastic hammer to see if it will come back to life. I have seen new starters and rebuilt starters not spring to life when bench tested. Tap on it, take it out and bench test it, if it simply will not work , grab your receipt and take it back where you got it and exchange it for a starter that does work properly.