In GM’s infinite wisdom, all GM trucks and SUVs used plastic disconnects for the heater hoses from 1999-2014. The problem with this is that over time, the plastic becomes brittle and breaks off. Because the connector breaks in the middle, you can’t just simply slide the hose over the heater barb and toss on a worm-clamp. Instead, you have to remove the remaining plastic connector.
The plastic connectors are available from your local auto parts store, or you can simply eliminate the connector altogether and use a basic worm-type hose clamp on the hose over the remaining copper tubing of the heater core. Whichever is up to you, but the real trick is getting the connector off the pipe. The disconnect tool is not readily available, in fact, you have to pay $90 at a GM dealership for the simple plastic tool, or if you can find a Snap-On truck, they also have them for a similar price. The other option is to carefully cut the broken connector off. This is very important: extreme care must be taken when cutting the connector, because too much shaking can break the heater core. These vehicles are incredibly difficult when it comes to changing the heater core. It requires removing the entire dash, and that is an 8-10 hour process.
The disconnect tool works by releasing the spring fingers on the inside of the connector. The small plastic tool folds around the backside of the tube, and is slid into the connector until the fingers are released. Then the connector simply slides off the pipe.
Cutting the disconnect can be done using a hand saw with a hacksaw blade, or with a small air-powered reciprocating saw. The key to cutting the connector is to make one straight cut across the top and another slice across the bottom, splitting the connector in half.
When one connector breaks, the other is usually not far behind. You should replace both connectors at once to avoid a repeat situation. One of the hoses has a plastic Y on it, one hose goes to the heater core, one comes from the radiator overflow canister, and the other side goes to the water pump. You can replace this Y with one that does not have bonded hoses, or you can reuse it.
Replacing GM plastic heater hose connectors is often an emergency situation, where the hose has broken and left you on the side of the road. It is not a bad idea to preemptively attack this problem and replace them before one breaks and leaves you stranded.