A More Efficient Way To Write This Method

Hi Experts!

Thanks for reading this.

There has to be a more efficient way of handing the string manipulation.
One thought is it use StringBuilder and passing it as ref..
Each time the method is called it creates the parameter (StrTemp), if I'm not mistaken.
The following method (ConvertStringWithSomeLogic) gets called 130K times and it takes 2+ hrs to complete..

Here's how the method is being called:

private static void InsertIntoDBTable(List<Model3> MdlCombine)
{
    SomeDB db = new SomeDB();
        foreach (Model3 m in MdlCombine)
        {
            Model3 st = new Model3();
            st.packagecodeid = ConvertStringWithSomeLogic(m.packagecodeid);
            st.STARTDATE = (m.STARTDATE);
            st.ENDDATE = (m.ENDDATE);
            db.Model3s.Add(st);
        }
        db.SaveChanges();
}

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Here's the method being called:

      private static string ConvertStringWithSomeLogic(string StrTemp)
        {
            string strReturn = StrTemp;
            try
            {
                int IntFirstDash = 0;
                int IntSecondDash = 0;
                GetDashPos(ref IntFirstDash, ref IntSecondDash, StrTemp);

                string strFirstSegment = StrTemp.Substring(0, IntFirstDash);
                string strSecondSegment = StrTemp.Substring(IntFirstDash + 1, IntSecondDash - (IntFirstDash + 1));
                string strThirdSegment = StrTemp.Substring(IntSecondDash + 1, StrTemp.Length - (IntSecondDash + 1));

                //CONVERT THE FIRST, SECOND, THIRD SEGMENTS
                ConvertFirstSegment(ref strFirstSegment);
                ConvertSecondSegment(ref strSecondSegment);
                ConvertThirdSegment(ref strThirdSegment);

                strReturn = strFirstSegment + strSecondSegment + strThirdSegment;

                if ((strFirstSegment.Length < 4) || (strSecondSegment.Length < 3) || (strThirdSegment.Length < 1))
                {
                    strReturn = StrTemp;
                    //write msg to event log with StrTemp in it
                }
            }
            catch ....            
            return (strReturn);
        }

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Here are the Convert Segment methods:

        private static void ConvertFirstSegment(ref string FirstSeg)
        {
            if (FirstSeg.Length == 4)
            {
                FirstSeg = "0" + FirstSeg;
            }
        }

        private static void ConvertSecondSegment(ref string SecondSeg)
        {
            if (SecondSeg.Length == 3)
            {
                SecondSeg = "0" + SecondSeg;
            }
        }

        private static void ConvertThirdSegment(ref string ThirdSeg)
        {
            if (ThirdSeg.Length == 1)
            {
                ThirdSeg = "0" + ThirdSeg;
            }
        }

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TIA!!