Put in a new master cylinder and the brake booster and bleed the brakes..... brake still not catching... goes almost to the floor.... What next? (2006 dodge grand caravan)

If it goes to the floor and no brake warning lites or anything comes up on the dash, check the brake booster--engine vacuum and vacuum to the booster. Just my opinion. The master cylinder usually bolts to the booster.

You still have air in the system.(not bled properly) If you let the Master cylinder drop down to nothing then you need to bench bleed that before bleeding the lines again.

First of all, I hope you got a new master cylinder with your disc brake kit. A new master cylinder should be bled before connecting the brake lines and then never allowed to pull in air during the rest of the bleeding process. A couple of fittings ans hoses should have come with the new master cylinder [see the kit listed for a picture]. If the master cylinder has an air bubble, you won't be able to properly bleed the rest of the system.
For the rest of the system you can make up a small catch bottle like the one pictured in the one man brake bleed kit; make sure the hose goes tot he bottom of the catch bottle. You have to cap the master cylinder reservoir before pumping the brakes or fluid will squirt out and all over; brake fluid is a like paint remover. Then start with the brake farthest from the master cylinder and bleed fluid out by having a buddy pump the brakes while you hold the catch bottle above the bleeder port so no air gets back in. [hint, put some pipe teflon tape on the outer threads only, not the inner end of the bleeder screws to seal the threads]. Check the master cylinder level often! If the brakes still are spongy after the first round of bleeding, have a buddy pump up the brake pedal with the bleeder screw closed and hold pressure on the pedal; you then open the bleed port until the pedal goes to the floor; have your buddy hold down the pedal until you close the port. Repeat on all brakes until the pedal is firm.

the reason may be : the brake booster is lack of pressure.

You probably need to start over...1st by bench bleeding the master cylinder...(you can do this on your truck...review the bleeding instructions...after completing this you need to be sure the master cylinder is full of brake fluid...you will need a helper...but your next step will be to bleed each wheel brake caliper or cylinder. Start with the right rear, next left rear, then right front to drivers side front...(farthest away to start) you may have a brake fluid leak...if not, your pedal pressure should continually raise...Hope this helps.

Check all the calipers and wheel cylinders

Check the vacuum booster first
Shut the car off after it idles for 3 minutes
Apply your foot on the brake and hold
If the pedal seems hard at first and did not go down all the way keep your foot on it for two more minutes
If the pedal gradually goes down to the floor the brake booster is leaking
If not start the car and let idle again
\With the car still idling step on the brake pedal again and hold
If the pedal goes to the floor in a second the master is shot instead

You changed the master cylinder and vacuum booster and have no leaks anywhere, but did you bleed the entire brake system after you did this work? A little bit of air in any of the lines will make the brakes ineffective.

It's very possible to be the master cylinder, the o-rings on the piston could be worn, letting the fluid seep back through instead of getting full pressure through the lines. Could also be the brake booster.
Try changing the master cylinder first, which is cheaper and easier, and see if there is a difference, you'll need to bleed the brakes again.
To check the booster,
With the engine off, pump the brakes until the pedal is hard, then hold pressure on the brake pedal and listen for air escaping, or the pedal goes slowly to the floor, Do that after the master cylinder has been changed, at least that will be eliminated.

check your brake booster vacuum pipe for leaks otherwise it sounds like your brake booster has failed