Why do i have a hard brake pedal when off, soft to the floor when its running?

You have air trapped in the braking system somewhere. Have you bled the system thoroughly at all four wheels?
Have you changed the front calipers recently. Many years ago, I helped a friend mount new calipers on his vehicle, and we put the new calipers on the wrong side -- right one on the left side and vice versa. In this configuration, the bleeder screw wound up on the lower portion of the caliper instead of at the top, where it needs to be to allow trapped air to come out. Just a thought.

This sounds like a vacuum or hydrolic issue. If The pedal is spongy soft while its running it indicates air in the brake line, or faulty master cylinder, or faulty brake booster. A faulty master cylinder would get hard after a few pumps of the pedal. Since the pedal is hard when it is shut down, it makes me lean toward the brake booster.

bleed the brakes again . start with the rear right wheel then rear left then right front . do it several times and ensure there is no air in the system

possiable brake booster. if you hear a hissing sound and truck runs rough if not possiable master cylinder.

check cylinder brake

the leather inside master cylinder is leaking. Buy a kit or a rebuilt from parts store.

bad master cylinder.. normal for pedal to get hard while pumping pedal with engine off.

you may want to try bleeding them while it is running

when you push pedal hard & pedal goes to floor does brake light come on?
assuming brake fluid leval is ok & didnt run empty have you checked for a leak?
pulling all wheels & inspecting brakes,cylinders, calipers,& lines for leaks.
does the pedal pump up & feel ok with engine running?if so there is air in the system
if it does'nt change the way the pedal feels & no leaks are found & brake linings are ok & adjusted
properly than your master cylinder is leaking internally & needs to be replaced

First check each wheel brake cylinder for small leaks. If no leaks then the brakes have not been bled properly. Liquid will not compress like air, thus the reason pumping the pedal makes the brake pedal come up. If you had all of the air out of the lines then you pedal would not be soft. With your pedal going to the floor either there is air in the lines or fluid is slowly leaking.If it is a small leak on one of your wheel cylinders, it may be hard to detect without pulling the wheels off and looking. Small leaks on your wheel cylinders may never drip off of the car.