Improving VBA Loop speed

Hello all,

I am trying to improve the speed of my loop macro because my loop macro is very slow to run a large database, over 3000 rows.
Is there any way to improve my loop macro? I have attached an example.

I would be appreciated with your help. Thanks.

Sub Sample()

Dim lastRow As Integer
'Dim SourceWB As Workbook: Set PAASourceWB = Workbooks.Open("C:\Users\user\Desktop\Src.xlsx")
    'SourceWB.Sheets("Src").Copy Before:=ThisWorkbook.Sheets("PROCESS")
    'SourceWB.Close
Dim TargetWB As Workbook: Set PAATargetWB = Workbooks.Open("C:\Users\user\Desktop\VBA_Help_Sample.xlsm")
Dim lRowCount As Integer, i As Integer
Dim v As String
v = "1st_Run"

Application.ScreenUpdating = False
Application.Calculation = xlAutomatic

Sheets("Tgt").Range("B6:XFD1048576").Delete Shift:=xlUp

With ThisWorkbook
lRowCount = Sheets("Src").Cells(Rows.Count, 1).End(xlUp).Row
    For i = 1 To lRowCount
        .Sheets("PROCESS").Range("i_Num") = i
        .Sheets("PROCESS").Range("B6:H6").Value = .Sheets("Src").Range("A" & i + 1 & ":G" & i + 1).Value
        .Sheets("Tgt").Range("F" & i + 5 & ":J" & i + 5).Value = .Sheets("PROCESS").Range("D4:H4").Value
        .Sheets("Tgt").Range("B" & i + 5) = v
        .Sheets("Tgt").Range("C" & i + 5) = .Sheets("PROCESS").Range("F3").Value
        .Sheets("Tgt").Range("D" & i + 5) = .Sheets("PROCESS").Range("C6").Value
        .Sheets("Tgt").Range("E6:E" & i + 5).Formula = _
        "=CONCAT(B6," & Chr(34) & "|" & Chr(34) & ",C6," & Chr(34) & "|" & Chr(34) & ",D6)"
    Next i
End With

Application.ScreenUpdating = True
Application.Calculation = xlManual

End Sub