Unknown Engine trouble

Hey guys, I have a 2000 chevy blazer 4wd with 99k on it. I have a few small issues that I think may be related so any help will do. One day my car sputtered and misfired so i checked the code and it said misfire cyl 4 so i replaced all the plugs and it still misfired but this time it was a random multiple misfire. My engine seems to run ok but its almost like it losses pressure at times and struggles to get up to speed. I also have a rattle on the right passenger side that i hear when i go to a dirt road on any rough surface. And last my muffler sounds like its going bad but all inspections look good. Any idead what the issue is and if its all related? I.e bad cat converter

A random misfire can be caused by a lot of things such as spark plug wires, cap and rotor. If these are original, time to replace. If the fuel filter hasn't been replaced recently, I would do that also. A bad fuel injector can cause a misfire, but usually it stays on one cylinder. But water in the fuel can cause a random misfire.
If you suspect the cat or muffler is causing the rattle, let the vehicle sit for a couple of hours (to cool down), crawl under it and give each a bang with your fist. They are both known to rattle when bad.

1.) Tuneup
2.) Search for clunk fix.
3.) Go under your truck when it is DEAD COLD and slap the underside of the cat and the muffler hard with the flat palm of your hand and listen for a loose rattle.

Thanks guys, replaced filter and bought spring washers and all is fixed!!!

Might as well do a tuneup.

spring washers ?

For his clunking hood.

ahhhh..........
i also had a similar prob...replaced the fuel filter....
loud whine from new pump...is kinda quiet again....
and power is back to normal.