P0300 Requesting Advice

[Hair]

1998, GMC Sierra, 2WD, 140k miles, 305 Vortec
Drive it every day, no issues ever, all stock.
It started missing on me, and the ONLY code that it shows is P0300.
All cylinders are getting fire.
The plugs look fine (#3 slightly wet/smelled like fuel, but looked good other than that.)
As I pulled plug wires while running, it seemed like the #3 didn't make much of a difference, but when I pulled it out and laid it against the manifold, as the truck ran, it was firing good. So I'm thinking that fuel injector may be bad.
Every cylinder has 190/195 PSI.
I do not see or hear any vacuum leaks. (Tried my best to fine something like that.)
At this point, I am thinking that it is probably the spider fuel injector assembly.
Before I start taking the upper intake off, do you guys agree, or is there something else I can check to make sure before I spend a day working on something that aint the problem? Any advice much appreciated. Thanks in advance.