query tuning issue

I created a functional index on "sum(coalesce(INDICATED_REVENUE,0) - coalesce(ACTUAL_REVENUE,0)) "  in query below query but still its very slow , what else can I try ?

the stats are current

select          

sum(coalesce(INDICATED_REVENUE,0) - coalesce(ACTUAL_REVENUE,0))      

from TAB1 t      

where t.tid = '925914455'            

and t. PM = '7'            

and t.Token is not null