I just completed the same repair on a 94 Suburban, 4x4, 1500. I imagine the truck is similar.
The box housing the heater core is under the dash on the passengers side. There are 6 screws which hold the bottom of the plastic box in place.
I used a 1/4 drive, 1/4" socket and easily remove 5 of 6 from the bottom. The 6th is located on the side nearest the firewall. If you pull the carpet down and poke around with your finger in the tightest spot you can reach you find the last screw. It's tricky to remove.
Once you remove the cover from the bottom you'll see a sinlge clamp that holds the core.(Don't remove it yet.)
It pays to drain the fuild level down below the hoses which feed the heater core.
There are two hoses; one is 5/8" and the other 3/4". Buy a couple feet of each and 4 new clamps. The new heater core may have a slightly different clamp to hold it in place.
Remove the existing clamps on both ends of the hoses. Slice the hoses along the axis of the tubes with a utility knife. Use pliers to peel the hose back and remove. (A little more fluid will drain off)
With the hoses removed match and cut you new hoses to length.
Remove the clamp on the heater core and remove the heater core.
Get someone else to hold the new heater core in place while you attach the new hoses and clamps to the heater core. ( They can push it forward to make it easier to get the hoses in place.
Next have them position it as it will be once fastned again with the clamp. Connect the other ends of the hoses and tighten all clamps.
Now clamp the new heater core in place.
Add some fluid, start the truck, turn on the heat, and watch the flow through the radiator with the cap off. Continue adding fluid until the level remains constant.
Cap the radiator.
Reinstall the heather core plastic cover. It's not easy, but you can get it back in place.