why is engine missing???

I have a 2000 silverado with 92000 miles. I changed the plugs with new ACDelco plugs about 3 months back. I noticed the engine started missing and running a little bad when under a load like going up a hill. It has gotten some worse. I checked the gap of the plugs but that seems fine. What is my next course of action?
thanks
tradrjeff

Now try replacing your wires. My 99' did the same thing replaced both plugs and wires now runs like new.

I was told that the wires were actually a coil wire and not traditional plug wires. I have looked online at Autozone and they don't list wires for a 2000 silverado. Any thoughts on this?

Stay away from AutoZone for plugwires,cheap and junk.Cheap plug wires are not the way to go.I know Carquest sells the plugwires,higher quality and are a lot better than AutoZone.Carquest plugwires are very good,the highest quality ones and you have to do it once.

The 4.8 (my engine) does not have a distributor, but it does have plugs and wires. Every plug has a wire that goes to it's own corresponding coil.