Hi, Conrad - It's probably best to come back here a few times over the next couple days and check on the progress of this thread.
The closest thing we have here in the database is this, a song by Bill Staines, but I don't think that's the one you're looking for. There's a really good Catholic hymn called "Praise the Lord My Soul," written by Jesuit John Foley in 1975. It is based on Psalm 103:

PRAISE THE LORD MY SOUL
by John Foley, S.J., copyright 1975

1. Praise the Lord, my soul,
Let fire and rain give praise to Him
Give praise to him who is merciful, slow to judge
Bless the Lord, O my soul
Bless the Lord, O my soul

2. Bless the Lord, my soul,
Let all I am give praise to Him
And not forget He is kind, He forgives our sins,
Bless the Lord, O my soul
Bless the Lord, O my soul

3. Merciful and kind,
He knows our ways, He knows we're dust,
And like the flowers that flourish, we soon must die,
Bless the Lord, O my soul
Bless the Lord, O my soul

4. Glory to our God,
Let all that is give praise to Him
Give praise to Him all you creatures who live His love,
Bless the Lord, O my soul
Bless the Lord, O my soul

Could that be the one you're looking for? I can post the tune if it is. If it isn't, please tell us more about the song so we can find it.
-Joe Offer-