As all your tables resides into same database I would use the SQL join, not the Qlik.
It would perform much better
SELECT ITMSNumber,Prioritization,SCA,DATALOADSTATUSID, LOADPRIORITYSTATUSID, morefields
FROM MPL.dbo.tblSTRATEGY a
inner join MPL.dbo.tblAPPINVENTORY b on ( join clauses goes here)
inner join MPL.dbo.tblBASIC c on ( join clauses goes here)
where loadprioritystatusid in (20,30,100);