Im installing southern pine flooring (3/4"x8"x12')I cut off my sawmill. I was going to use a shiplap instead of tongue n groove because it's easier to install. Using a date blade on a table saw. Can I use a finish nailer 18 gauge 2" nails? Floors have been kiln dried. Most of what Ive read say finish nailer is not good, but most people are using tongue n groove which require the angled nailer. Has anyone shiplaped flooring?

I've never installed ship lap flooring, but you could still use a flooring stapler on the
"tongue" of the planks. I would use a quarter inch bead of the best poly-urethane flooring glue that comes in a sausage that uses a special gun to dispense the glue.
You would then only need to top-nail one side of the planks on the edge where you are going to top-nail, usually about every foot along the board. I would recommend 8d casing nails instead of 18 ga. air nails.
The finish nailer does not pull the planks down, it will only hold the plank as it as when the trigger is pulled. If you do prefer to use a finish nailer, it would help to step down, placing a lot of weight on the spot where you nail, each time you pull the trigger. Some people double nail each time when using the finish nailer, "toe-nailing" both nails, placed at opposite angles, to help hold the plank as the glue hardens.

What's your reasoning behind the 8d casing nails, Pete?

Casing nails have a blunt tip so they don't split the wood as easily as sharp pointed nails. They don't drive as easily but punch through the wood without spreading the fibers. Casing nails have a counter-tipped head so as the head widens it pulls the board into place firmly. Driven by a hammer so you get the nail head flush with the surface without denting you are ready to set the nail as the plank meets its surface of the sub-floor.
Blunt tipped countersink head that are "cement" coated are as good as the come.
These are much better than bright nails and hold 30% better.