I notice the name you chose for the alias (SP2013-SQL2014) is the same as the actual SQL server name. Normally, you wouldn't do this, since part of the reason for an alias is to de-couple the real SQL server name from the name we use to reference it. But anyhow, can you edit your XML to display as follows instead (although it really shouldn't make any difference):
Brian
<Database>
<DBServer>SP2013-SQL2014</DBServer>
<DBAlias Create="true"
DBInstance="SP2013-SQL2014\MSSQLSERVER"
DBPort="" />
<DBPrefix>AutoSPInstaller</DBPrefix>
<ConfigDB>Config</ConfigDB>
</Database>
If this doesn't work, I would compare your version of the XML that did work prior with the newer version that's causing trouble to see where the discrepancy could be.Brian