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May sound crazy. But, try doing your cardio training while wearing an airpack. Make it a little tougher by wearing the face piece. Tougher still by actually breathing air from the bottle.

It worked for me. And I lost some weight, which helped even more.

When I started in the service, I immediately started to read about skip breathing and how to breathe.  I then applied it to the way I breathe.  I try to always breathe through my nose and I practice skip breathing all the time.  I agree with Tsmith, if you are having a problem with it then you may need to do some exercise with it on.  I have read that that helps.

TSmith gave a good idea. Do cardio in SCBA, and focus on your breathing. Practice controlled breathing, which is slow-deep breaths. You would think that deep breaths would consume more air, but, let's have a quick physiology lesson.

The breathing reflex is triggered by the presence of carbon dioxide ( co2 ) in you respiratory tract ( ever seen sponge divers or free divers appears to be hyper-ventilating before ascent ) what they are doing is flushing the co2  from their lungs so that the breath reflex will not be as quickly triggered. I do not recommend this, as practiced un-safely it can lead to dizziness and unconciousness.

But, what I, as a firefighter,  do is take SLOW deep breaths, and displace as much co2 as possible with each breath, this causes the breath reflex to be triggered less frequently, and thus uses less air. It is safe, I've done it for years, and use less air than ( a lot less ) some guys 1/2 my age. Granted they are less experienced and excitement will cause you to breath faster.

Short-shallow breath leave more co2 in your system and you breath much more rapidly. Your legs use more oxygen than any other muscle group, keep this in mind during your work-out, and your actual use.

I hope this helps. With time and practice, you'll definitely improve.

I am a bird breather. I can dive an hour and a half on 3000 psi and for 45 minutes and still come up with 1000- 1350 psi, sometimes more of less. When we go SAR training  trailer I can go 2 times on 1- 4500 psi bottle and still have 500-1000 psi.  This may sound funny but practice humming. Lay on your back and  take a deep breath to your diaphram. Let the air out slowly and while you are humming. Making sure your mouth is close and you are feeling the vibration on the roof of your mouth and the air passing thru your nose. Same as metered breathing when you sing to get to the long notes just with humming and nose air instead. Also cardio exercise, bicycling, swimming and jump rope.

i use up my air faster than people twice my weight...i have a fast metabolism and thus am prone to heat stress.  also am a mouth breather because of allergies.  even kung fu breathing methods don't really help when your sinuses are clogged all the time.  but despite it all, i love being in Level A.  makes me feel like i'm accomplishing something.

Thank you very much to those who took the time to answer my question. They were all great suggestions and I will try them all and see what works best for me. Thanks again.