Problem with copying volatile data values to rows of a google sheet

Question

I am trying to convert an old Excel VBA program to Google Sheets for projection 30 years of financial results. The key issue is the VBA Excel sheet haw a row (a1:ad1) of (30) cells that each contain the volatile function Rand() to generate a random number in each cell through each of 1000 loops:

In each loop these cells 1) reset their random number, then 2) some rows of calculations are made based on the new random numbers, then 3) then a resulting row of 30 new values in copy-pasted (values only) to another part of the sheet so the individual results can be statistically analyzed.

The copy-paste in google sheets is too slow and I hit a 6 minute execution time out, so I am trying to accumulate each loop into a single 2D array, each row being one of the 1000 loop results in 3 above,then write the entire array back to the sheet at once. To get the 30 cells to recalc, each time I read a row, I force a new value to be set in a single cell of the spreadsheet at the beginning of each loop. That seems to work, but trying move the data from the row to the accumulation array and then writing the values back to individual rows in the sheet at once, I always wind up with arrays the have too many dimensions some other problems getting the data back to the sheet as a 1000 x 30 range of static data.

Here's the basic outline of where I am so far after many variations of this :

        function test1(){
          var sheet=SpreadsheetApp.getActive().getSheetByName('UST_Results'),
           range;
           var values=[];

          var LargeArray= Array(new Array()) //new Array()

          for (var i=0;i<3;i++) {  // using a small number (3) rows to get it work

              values =getRandRow(sheet)[0][i];

              LargeArray(LargeArray.length) = JSON.stringify(values)

         };
        };

          function getRandRow(sheet)  {

               var values_array =[];
           let myData =[];
           var cell = 0;
           // force the Rand() to recalc before getting the next copy of A1:Ad1
              for (var i=0;i<1;i++) {
                  var cell = sheet.getRange(i+5,1);
                  cell.setValue(i);


                  SpreadsheetApp.flush();
             }

                 range = sheet.getRange('A1:ad1');
                 values_array = range.getValues();
                 myData.push(values_array);

                 return myData;

               }

A picture of the sheet testing with just the rand numbers and not the derived row.

enter image description here