SQL query tuning issue

Question

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