What return this ?

SELECT COUNT(*)
FROM icitrf
WHERE (dtrs BETWEEN '02/01/04' AND '03/26/04') 
AND (cwhouse BETWEEN 'WAL0000' AND 'WAL9999')

Who is Clustered index ?

try to define a single index for
(best choice is correlate with data distribution) :

dtrs,cwhouse,citemno
or
cwhouse,dtrs,citemno