new pads/rotor: really soft brakes

I changed out my front brake pads and rotors on my truck this afternoon. Now I have to almost put the brake pedal to the floor to get my tuck to stop. I was sure to "pump" the brakes a few times before driving it around, so that the pistons would expand, but after driving around for 10-15 minutes, the brakes are still really soft. I haven't lost any brake fluid that I know of....
Any ideas?
Thanks in advance.

did you bleed the brakes?

Did you clean the new rotors with brake clean? New rotors will have anti rust coating on them that can contaminate the pads. Otherwise cheap pads sometimes just take a few hard stops to break in.

I didn't bleed the brakes, just changed out pads/rotors. The pads and rotors are both "budget" pieces, but I wouldn't think that that would make the braking any less firm (it might just make it take a little longer to stop until they're broken in). Should I go ahead and add a little brake fluid to see if that helps?

If you did not loosen any of the lines you should not have to bleed them. The new pads have to conform or break in to the new rotors. sometimes they feel soft until you do a few hard stops, do not overheat the rotor when braking them in. Go to an open road with nobody around do a hard stop, drive for a while to let them cool. Do that 3-4 times and they should feel better if that is the problem.

If you repeatedly pump the brake pedal when you're stopped, does it 'pump up' to the point that you finally get a high, firm pedal? If you release the pedal wait 15 seconds and then depress it does it go to the floor again? If you answered yes to both of these questions, you have air in the system and you have to bleed your brakes. It's as simple as that. If the answer to the first question is no, then you have a problem somewhere. I don't want to sound critical but IMHO, one of the worst things you can do, especially if you have ABS, is to just compress the caliper piston when you install new shoes. This just forces old brake fluid back into the system. I always open the bleeder and drain the old fluid when I compress the caliper.