Misfire 2005 GMC Envoy XL cylinder 5

cylinder 5 missfire low compression

Rings or Valves with valves more likely. Have a wet and dry compression test done. If the wet compression is a lot higher, it is the rings.

So I looked up the specs . . .

For the 4.2 liter straight 6, which I assume you have, it’s 215psi.

Just how low is the compression?

Without even being there, my gut feeling is valve train

I also suggest a cylinder leakdown test. I suspect you’ll have quite significant leakage, and it’ll be from the intake valves.