The pedal sinking to the floor and being able to pump it up is a classic case of air in the system or master cylinder. With a new MC, I'd bleed and bleed and bleed it to see if I could get the air out.

 

I have a 2011 crewcab had real good pedal but had a warped rotor,installed new front rotors and pads now pedal is spongy and slowly sings toward floor,truck will stop pedal just not right,anyone have this problem?

 

Before anyone "informs me" how old this post is, I'm aware of it's age. After re-reading it I saw no concrete answers offered, only more suggestions where to look. I had commented that when I solved my issue I would post the results, here they are:


After coping with my own "pedal sinking to the floor" issue for quite some time now as I previously mentioned in the comments above.
Last week my truck developed a leak at the ABS unit, I located a used unit with a warranty from a local salvage yard for $150. A new unit from the dealer is well over $1000 and while I like my truck I am not willing to spend 1/3 of it's value to fix the brakes.
My brother and I installed it along with new lines from the master over the weekend.
I'm happy to report that there are no more leaks, and the mysterious sinking pedal is gone!

If I had to guess what was wrong, the ABS had an internal leak causing the pedal to sink without losing fluid. Eventually it got bad enough to leak out of the unit.

 

Thanks for the feedback. Knock on wood. I've never had an ABS problem.

 

Well, I'm still having that same issue after spending >$600. I'm not mechanically savvy, so I been living with it as it only happens after complete stop. One of these days, I may have to pull out a book and get dirty myself.