Need a little help please!

[sleepingbag]

Hello men, having a confusing little issue with the truck today, need some experts input. Started truck up this morning no problem, let her warm up for a bit, and went to take off... killed the motor...no biggie, BUT when I went to restart got a few weak whirrr, whirrr, whirrr sounds from starter, but no start! Came back a few hours later and truck started like it was brand new! Battery strong, alternator fine(per my tester) what could have caused this? No temp gauge so I dont know how hot it was running, thermostat prob? Thanks for any help in advance!