And you're sure the nails are feeding properly? The piston will make a mark in the wood like a nail has been driven, even when the gun fires a "blank".

What kind of gun, what brand of nails, how many psi?

1.5 in hes of maple is going to put premium on the nailer and air pressure.

If the grain in the molding is at an angle to the face you are nailing (rift sawn) it may well deflect the brads (especially if is a harder maple).

What gauge are the brads?

You may need a bigger brad, or break down and use screws (pre drill and a right angle attachment on the drill).

Even if they were going in straight a 2" brad (18 ga?) is pretty marginal for attaching stock that big. I'd use a 15ga finish nail at least 2-1/2" long. More of a hole to fill, but it won't fall off.

I have used 18 and 16 gauge finish brads/nails in all kinds of wood molding. Now and then there will be a deflection problem, but have never seen that on every nail.

The application, mas I understand it, is adding decorative trim on the bottom edges of wall mounted upper cabinets. That means the back side of the cabinet lip is open---anything sticking out is going to be a hazard.

In my experience, a 15 gauge nail is too large for that particular application. That size can easily split the edges of the cabinets when used that close to the edges.

In fact, were I doing that job, I would be using an appropriate adhesive and just a few 18 gauge brads.

I have Porter Cable nailers(all 15 or more years old) and use Paslode finish nails/brads.

Thank you all for the advice. We will attempt again this weekend!

And no "blanks." Nails were shooting just fine, but not through the 1-1/2" of maple.

I much prefer screws as they draw tight and cannot work loose.
Even if you must add a strip to the back of the faceframe to fasten to. You can pin it with 16 ga. finish gun and instant glue, then locate the screws as best you can, but the pins/glue hold it in alignment while you do this.
Casey