I would say its your water pump or the seal went bad. My suggestion is to drain the coolant and pull out the water pump and replace the seal. If you have he money you might want to change the water pump while your at it just to rule it out if your still having problems. Other than that cheap things to fix are the thermostat. If that doesn't work it may be your hoses and worst case it will be the radiator. I would just fix the cheapest things first since they seem to go first. Good luck!
Just had mine in the shop for a leak too. Sounds like it may be your water pump - it has a weep hole you should be able to find looking up from underneath the truck on the water pump housing.
My problem was a bad gasket at the lower elbow which connects to the pump and a bad thermostat housing gasket.
Got a coolant flush and refill since it was in the shop, with the above repairs, totalled around 550.00 -
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