just replaced rear rotors and calipers. went to pump brakes after bleeding and blew out the main brake line to the rear (rotted out). Replaced that and bled all brakes again with engine off then with engine running.
Pedal still goes to the floor when the engine is running. I'm about at the end of my patience with this one.
Anyone have any suggestions before I have it towed to a garage?

 

Are you sure you got all the air out of the line? Do you get a hard pedal when the truck isnt running? I went through all this when I blew my rear brake line. I ended up replacing all the lines cause after I fixed one another one started to leak.

 

I was pretty sure I got all the air out, I pumped allot of fluid through the lines inthe process. I get a hard pedal when the engine is not running but once i start the engine the pedal goes to the floor. someone suggested bleeding the master cylinder and ABS then go through all the wheels again....

 

You can try bleeding the master cylinder but I dont think that is your problem. I think your problem is in your brake booster

 

I agree with the previous post that there could be air still in the system. If you didn't have the dropping pedal before you blew out the line, then most likely it is air. The bleeding sequence for your truck is right rear, left rear, right front, left front. If air got back into the system this might be something you don't have the tools for if your truck is equipped with 4-wheel ABS. The system runs a modulator self-check on each key cycle that runs the modulator pump. If there is air present, it will ingest it into the pump circuits, then discharge some at each pump cycle.
A bi-directional scan tool would be used to run a bleed function on the ABS modulator. The sequence would be bleed the base brakes as described above, then run the scan tool bleed sequence, then repeat those steps until all the air is removed. There is only a small distance that a booster will allow the pedal to drop if it isn't functioning properly. It adds substantial force to the pedal application so any air would be much more noticeable with the engine running.
Any time there is ABS in the system it is highly recommended that you open the bleeder as the caliper pistons are pressed back in. This will keep any debris and contaminated fluid from being pushed back into the ABS modulator....which can be expensive if you're not lucky.