The GMC Sierra has had both distributor and distributorless systems since its inception in 1997. If your Sierra has a 4.3L, 5.0L 5.7L or 7.4L engine, it has a distributor. If you need to replace the distributor, here's how to do it with a few basic tools.
Remove the plastic cover from the engine block with a wrench, then let the spark plug wires lead you to the distributor. It's at the back of the engine block.
Remove the negative cable from the battery at the side of the engine compartment; carefully pull the spark plug wires off the distributor cap so you don't damage them. Use a screwdriver to take off the coil leads from the distributor and the electrical connector at the bottom of the distributor.
Loosen the clamps and take off the distributor cap. Mark the parts to align the rotor position to the distributor housing and the housing to the engine block. This will help replace parts correctly during distributor installation.
Unbolt the distributor hold-down bolt with a wrench and remove the distributor from the engine.
Install the new Sierra distributor, aligning the marks for proper seating in the engine block. When ordering the distributor, give the parts dealer your model, year and engine size. You can order part number A1841639 from Parts Train for a 4.3L engine.
Re-install the distributor hold-down bolt. Replace the distributor cap and put the clamps back on. Attach the electrical connector at the base of the distributor, put on the spark plug wires and coil leads, and hook up the negative battery cable.