Ryan,
You may have splashed some water or coolant. So try starting to see if you have a leak and if so where.
Some thoughts of where leaks can happen at the front of your engine.
1) Water pump housing
2) Water pump seal
3) Thermostat housing (Next to water pump and altenator)
4) Upper or lower radiator hose (Did you remove them from the engine side? Maybe it did not seal up correctly.)
5) Heater hose
6) Oil cooler - Long shot but one side is up on the drivers side close to the front of the engine. Known to leak over time.
7) Headgasket - Not sure why a flush would cause this unless you shot air or water line pressure into the system. (Most radiator caps only let the pressure build up to 8-14lbs, once tired less than that. So shooting air/water from a compressor, or street water pressure of 80-110 PSI is not a good idea.
I would try one of these two things.
1) Run it and look around for a leak. No leak, likely you just splashed some water or coolant all is good. If you do have a leak and all you can see is water dripping on the ground. (Things are in the way of getting a look.) Borrow or buy a decent video borescope to see where the leak is origninating from. (Try a mechanics mirror as a cheaper option.) Also look for any heavy corrosion or a coolant stains. They will give you a good clue where it leaks if only interminttently.
2) Intermitent leak - Buy one or see if your local parts store has a loaner radiator tester. Pump up to say 10psi with engine warm and look for a leak may just be a couple of drops, then go to 13psi and look again if nothing at 10psi. I would not go too high since you could make something old and crusty give out. (Headgasket, hose, seal, oil cooler o-rings, etc.) Stop and monitor for leaks frequently till you find one. Also when your radiator is cool open it, top it off, it should stay full (Or very close) if you do not have a leak.(If you have a good radiator cap.) If you do have a leak you will see your overflow tank (If working, no cracks.) or radiator coolant level is getting lower in time. You will usually know when you have a leak, you will smell coolant in the cab or when standing next to the truck when you park.
All the best.