When I start my truck and get going, the temp gauge gets hot then gets back to operating range once i'm driving for a couple minutes. What could this be?

air pocket in cooling system..short in system , bad gauge..bad sender.. (fans off...you said goes ok when driving... you .dont need fans when air is passing thru the system when your driving,,, unless they are helpers in your cash a silverado your fine....could even be a funky thermostat .. FILL SYSTEM BLEED FIRST>

jim,come on mannnnnnnn...but i said that above.

Lazy cooling fan or thermostat. If it is losing coolant and there is no external leak, uhh, that's bad.

and the winner is .......?

OH! OH! OH! Me, make it me. LOL. Let us know what fixes it.