Work on maximal holds. This grip cycle brought me from being able to handle holding 600 lbs to being able to hold onto 950 lbs. Grip is never an issue now. A1 = Barbell holds (heavy as you can hold for 10 seconds), A2 = pinch plate holds - pinch the plate between your thumb and 4 other fingers. Once you can do say a 10 lb plate, add a 5 lb plate, once you can get up to 25 lbs (don’t use a 25 lb plate, use more smaller plates to make it thicker which makes it harder and develops grip better)

Lastly, if you want a strong deadlift - a true deadlift then you need to develop your grip. Lose the gloves (makes the surface area greater thus making it harder on your grip). Use chalk (carbonate based works best). No straps for now. I had this same problem when I was stuck around 500 on my deadlift and I took the time to reset, fix my grip issue, and I’ve never had a grip issue since. A benefit of a strong grip is that it makes EVERY LIFT STRONGER. Your hands are your point of contact