Odd that you're finding the primary fire feeling inconsistent - the pellets do fixed damage, and it fires 3 tics faster, but it has slightly more spread than the vanilla pump shotgun. I'll see what I can do about that.
I wasn't aware that UZDoom had a Pistol Start on map start option. It might not work because the extra firemodes are handled with inventory items and are not weapons themselves. In that case, you can always use IDCLEV, or level warp using the console.