Elbow Pain from 5-3-1 Deadlifting

I have been doing Jim W’s 5-3-1 program and things have been going very well. Now that DL is over 400, my elbow is constantly in pain afterwards. I have noticed that it is terminal elbow extension that irritates things and the conventional DL with alternate grip may be the cause.

Loaded pull-up over 70 pounds are not painful at all. It has to be a form issue and reversing the grip may be necessary. Has anyone experienced this? Is there any suggestions that can be made to allow continued DL? Thanks

Is it terminal extension with the forearm/hand supinated or pronated or both that bother you?

Pain is definitely worse with elbow extension and pronation. There is also quite a bit of pain when reaching outward to pick something up like grabbing a weight to place on a bar.