hey can you tell me how you got to the core hoses? Did you go behind the tire?Not sure if you have the 5.2 or 5.9 or if they are different, but I just did this before changing my heater core in my 99' with a 5.2. TazRangos idea is probably better but what I did is below.
Take 2 pairs of vice grips or something equivlant, and clamp off each of your heater hoses about 8 inches or so away from the firewall (so you dont have to drain your coolant) leaving yourself enough room to pull them off. I duck taped the teeth on my vice grips as to not cut the heater hoses.
Once they are crimped (you will still lose some coolant out of the hoses so have some rags under the truck) pull the 2 heater hoses off of the inlet/outlet lines coming out of the firewall on the drivers side. I put quite a bit of muscle into mine and could not get the bottom one off so I had to cut it off, cut as little as possible unless you plan on replacing the hoses later. Pick up a heater hose connector for your size and 2 new clamps, only a few $$ at the parts store and simply connect the two heater hoses together. Mine are 5/8", but double check yours it should say what size the heater hoses are on the hoses themselves and thats the size connector you will ask for.
If I were you when done I would also stick your garden hose in either the inlet or outlet line on the heater core sticking out of the firewall and flush it out so its not full of coolant still. A quick search on heater core on here and you will probably find some pics of the lines crimped I know I have seen them. Top off your coolant when done.