In the spirt of debate, since we're doing the same program....
Are you sure you aren't starting too heavy on some of those warmup lifts? As Rippetoe says, they aren't supposed to tire you at all. For instance, doesn't your bench wear you down? I thought SS had all lifts start at 45lbs and scale up?
Also, In Practical Programming, Novice section, Rip specifically says deadlift is done for 1 set of 5 reps. In SS, I think he just eliminates the warm up sets and jumps in to work sets.
In my very limited experience with this, I was doing too much warmup and cutting into the work sets which is where the stimulus for growth occurs.
Also, I suggest doing subbing front squats in your weekly program of 3 squats. This is Rip's recommendation on page 162 of Practical Programming, where he moves to (for advanced novices):
and then changes it around slightly the 2nd week,
You can argue whether we are advanced novices but I think there are synergies between the back and front in terms of body position and technique. It will also really help with the O lifts later.