Running Total over 100k Rows - Not Enough Memory

Hi All,

I am trying to determine the running total for a messure called [Inventory Value].

It is too slow and will not process. 

Running Total = 
VAR InvRank =
        RANKX(
            ALLSELECTED(Inventory[ItemID]),
                [Inventory Value],,
                DESC,Dense
        )
VAR RunningTotal =
    CALCULATE(
        [Inventory Value],
        FILTER(
            ALLSELECTED(Inventory[ItemID]),
            InvRank >= RANKX(
                    ALLSELECTED(Inventory[ItemID]),
                    [Inventory Value],,
                    DESC,Dense
                    )
        )
    )
RETURN
IF([Inventory Value] <> BLANK(),
RunningTotal)

Sample Table:

I have on the order of 100 thousand unique part numbers. I am using all selected to record the information by BranchID. 

Note: no other visuals/reports have this problem. Everything else has less than a 480 ms load time after clearing the cache.