Experiment with every kind of DL form you can imagine....
Practice getting in and out of start position. One day I just went crazy on the barbell dropping down and gripping it getting into a position for double overhand, going up and down again switching to a mix grip, up and down rotate to the alternate hand mix grip...repeat 50 times. It looks retarded but helps to learn positioning. Like you I can get tired out just maintaining start so I want to be able to set up FAST.
Focus on the visualization and idea of a see-saw. It's kind of like the barbell pushing on you which in turn helps to bring it up. Hard to explain but that's when I felt my deadlift form "click" for me.
Semi-sumo is not a sin. Try it.
When setting up do NOT focus on your back...feel your ass getting into position and focus on that part of the set up while the back sets itself up.
Lastly, LOCK your lets. Find a YouTube vid by Michael tuchscherer on this.