Berin Loritschin Physical Fitness Stack Exchange • Recommends
On “Deadlifts - should my legs ache?”
…"the weakest muscles will ache the most".
The biggest issues from what I'm reading in your question and what I imagine you are doing is that:
You're hip hinge technique needs help
There's a good chance you have some excessive rounding in your lumbar as you fatigue
Another good resource would be Alan Thrall's video with 3 deadlift tips: link to this video
Some quick advice would be:
Do one heavy set of 5
Do 5 back off sets at 50 kg less of 3 (two less than the heavy set reps)
Focus on firing your glutes
Contract your lats before you pull
Stay tight until you have the bar on the ground
Don't be so gentle putting the bar down…