1998 Chevy Silverado Sputtering Backfiring

I'm a little lost with your timeline. When you say "there was a time when.", Does that mean it is still dying at red lights now? The first part where you said you replaced plugs, wires, etc and it misses, skips, and gets bad gas mileage. If the plug wires were put back on in the correct position on the distributor cap, and if none of the spark plugs were cracked while installing them (both of these are common things that happen when changing spark plugs and wires, even the best mechanics will do either of these sometimes), then I would be looking at the distributor cap and/or distributor.