Hello,
the Excel.au3 UDF is interacting with the Excel application. Maybe one of the authors can jump in to answer, if the speed is limited by this "Excel Remoting"? (See header -> author in excel.au3)
Quite a while ago I noticed, that using powershell to convert excel files to CSV files, then work with these CSV files, is to me easier and much faster.
Have a look at this free powershell module, that even doesn't need the Excel application to be installed:
https://www.powershellgallery.com/packages/ImportExcel/7.8.6
I use that one in conjunction with Autoit to process the data, that I need do plot to a temperature graph (image).
import-excel $XLfile -WorksheetName $WSName| convertto-csv -notypeinfo | out-file $CSVFPFN -encoding utf8
Maybe doing the replacements using regex line by line (instead of array-cell-by-cell) might speedup the procedure?
You also might look at the results, when placing in your loops some consolewrites to follow up the speed:
ConsoleWrite("ScriptLine: " & @ScriptLineNumber & ", $i = " & $i & @CRLF)