A deficit deadlift is a deadlift performed while standing on a weight plate or platform, usually around one to four inches high. It's used as assistance work for those that have trouble in the first stage of the deadlift. The increased range of motion also recruits more of the posterior chain and quads.
You can even get creative with it and use farmers walk handles on either side of your platform or plate. These really challenge your grip with heavy weights.
How you could stretch out a set by making use of the fact that you can give yourself a biomechanical advantage simply by changing your foot or hand position.
If your size and strength gains have stalled out, it's because you made things too complex. It's time to get back to basics and get strong... using only 4 reps.