Ok, I got 2 big glitches, one of which is annoying me a bit, the other is just straight up ruining my game. First one you've probably heared; as soon as I modded my weathered 10mm pistol, I get a grey screen that turns out to be a massive red box with an exclaimation point in the middle attached to my chest, and my gun goes invisible.
Next one makes me major rage. I was doing the "Birds of a Feather" side mission and it was going fine until after we killed the crazy dude. Simon won't move the body and the fourth NPC won't come, and when I go to try and deliver the package, Simon shoots me and it tells me I failed the mission. Also, my autosave is right where simon is just staring at the body, and my last manual save was 3 hours back at the Boulder City Showdown. I don't want to have to lose 3 freaking hours. Please help me.
Thanks, guys.

If you have a stealthboy on you you could try using it as soon as your game loads, then Simon won't shoot. Other than that, you may have to wait for the patch.

1st issue got fixed in the patch, 2nd one, don't know.