2003 F250 5.4L gas engine will not start when it is very cold out. Brand new battery and it turns over great but will not fire.

When it is 40 degrees out it starts no problem.

When it is 20 degrees out it will start after many cranks and using starting fluid into the air intake, then runs fine.

When it is 0 degrees out it will not start no matter how many cranks and using starting fluid.

I understand how the cold would affect a diesel engine but don’t know why the cold would affect a gas engine.

Any ideas to look for? Thanks