Most likely the cap you are trying to fit is 1.125 where you need a 1.062. You should get this joint DANA SPICER 5-7437X if thats the case.Bunch of great feedback in here. I need to make sure it was seated fully as it may not have been seated as much as I thought based on the comments in here. It does have the lock ring as you noted.
I'll measure the cup and cap and make sure they fit as it seems that's my problem.