If you're feeling that your lats are your weak point in your deadlift then solving this weakness is REALLY FUCKING SIMPLE.
You need to do 2 exercises:
1) Weighted Chin-ups [6-8 Reps]
2) Dumbbell Rows [15-30 Reps]
Go balls out on these exercises. Use straps so you can work your back more effectively. Pretend your 6RM Chin or your 20RM Dumbbell Row is more important than your Max Bench Press.
Use any Chin-up Grip you want. Just use the one you're strongest with. If you have a shoulder-width, neutral grip available then that's probably the strongest one. In fact you might not even need straps if you can use such a chinning bar.