Problems with spark plugs and wires

[Ridedo]

I recently replaced the spark plugs and spark plug wires https://mechanicfaq.com/spark-plugs-for-5-3-silverado/ on my 2002 Chevrolet Silverado 2500HD, on the way to autozone (approx. 4 miles away) to get my refund back for the warranty, the engine started a pulsing shake only when I idled in the parking lot. I knew it was a misfire and immediately thought I inserted the plug wires wrong. I took all 8 out and plugged them back in but it didn't help. I read the code P0300 which said 1 or multiple misfires,also a fuel pump code. I already had codes for my fuel pressure sensor, and knock sensor(which i was trying to avoid till I could afford it). The engine shake has progressively gotten worse to the point where I feel it while accelerating, and driving at a constant speed(losses power). My question to all of you, is what could cause a misfire after replacing spark plugs correctly? Could it be the fuel pump/pressure sensor causing the misfire? Or is it the coils? Is there a way to narrow down which cylinder is misfiring before replacing a bunch of other things? I just need the misfire gone so I can gradually fix the little issues. Any comments will help me greatly. I'm out of options other than replacing the fuel pump and hoping that's the main cause.
Thank you for your time