I've been researching this all day. From what I've read: - The low-drag calipers, which came on all 1/2 GMT400's, require a QTU (quick take up) master cylinder. - The QTU master works by using a large piston to send fluid to the calipers fast, then a smaller piston to build pressure - GM realized the mistake of using low-drag calipers, so they are not used on any other generation of trucks, including GMT800 - Rear drums seem to not require the 10lb residual valve - The leading/trailing rear drums are shit, and there's no easy way to upgrade them So, IF all k1500 trucks use low-drag calipers, that require a QTU master, and there were no low-drag calipers or QTU masters after 2000, is the whole master cylinder "upgrade" bullshit? Using a GMT800 master seems like it could be causing most of my problems: - It's a disc/disc master - It does not have a QTU feature - Front brake pressure builds late (explained below), which could be why my drums are slow to engage and seem to barely work The lack of the QTU feature could be the reason for the long pedal travel before my pedal firms up close to the floor; the small piston has to send enough fluid to the calipers before they start to grab the rotor because of the low-drag feature. The larger piston on QTU-equipped masters sends this fluid in a much shorter pedal stroke, so the GMT400 brake pedal initial "mush" is the QTU feature in action, sending fluid to the low-drag calipers. This mush is much longer with the GMT800 master, because of the smaller piston moving less fluid. Is there any merit to anything I just wrote? This is just my interpretation of all of the conflicting info I've read. Makes sense to me, but I have no clue what I'm talking about, and very well may be missing something. I do find it hard to believe that everyone that does this master cylinder "upgrade" has the same issues as me and ignores them simply because their pedal feels better.