Speed Up The Process..how? Alternative Way?

Good Day, please help me,
 i have a data driven site that displays computed data to a Complete Gridview, this is my problem, when i run my site, it all displays the informations and the gridview a i intended to. generally my site works fine BUT!!!!! my site have different levels of display, like this
Site 1:
it has 3 dropdown menus, dropdown 2 is dependent to dropdown 1 and dropdown 3 is dependent to dropdown 2 and the complete gridview is dependent to dropdown 3, it is a postback process of dependencies, i hope you get what i mean,
 
Site 2:
this is the same as the site 1 but this time, is has 2 dropdown menus only, and the complete gridview has a gridview in side of it thru details template.
 
Site 3:
almost the same as Site 1 and 2 but this time there will be no dropdown menus, only the complete gridview, but the gridview has 3 levels, the same level sa the level of dropdown menus in site 1, where the main gridview has a gidview below it and a gridview again below it and soon,
 
The Problem:
the site works fine but it runs super SLOW!!! specially in the Site 3, where it has to display and compute different gridviews from the complete gridview at the same time, sometimes it cause the TIME OUT EXPIRE.
that can i do to speed the process other than upgrading my server? is there an alternative?please help
for more info this is the SQL codes that i used in each level in the complete gridview
The highest level in the gridview of the initial display of the complete gridview:
 select rbu,count(distinct dslamname) as NumberOfDslam,
(select count(secode) from dslamdata as a where a.rbu = r.rbu ) as Capacity,
(select count(secode) from dslamdata as a where a.rbu = r.rbu and dnum > '1') as Used,
(select count(secode) from dslamdata as a where a.rbu = r.rbu and dnum < '1') as Remaining,
(select (select count(secode) from dslamdata as a where a.rbu = r.rbu and dnum > '1')*100/(select count(secode) from dslamdata as a where a.rbu = r.rbu )) as Utilization,
(select sum(dwlink) from dslamdata as a where a.rbu = r.rbu ) as Sold_Bandwidth
from dslamdata as r
group by rbu  
The Second to the highest when you would click on the +/- button in the complete gridview
 
 select aco,count(distinct dslamname) as NumberOfDslam,
(select count(secode) from dslamdata as a where a.aco = r.aco ) as Capacity,
(select count(secode) from dslamdata as a where a.aco = r.aco and dnum > '1') as Used,
(select count(secode) from dslamdata as a where a.aco = r.aco and dnum < '1') as Remaining,
(select (select count(secode) from dslamdata as a where a.aco = r.aco and dnum > '1')*100/(select count(secode) from dslamdata as a where a.aco = r.aco )) as Utilization,
(select sum(dwlink) from dslamdata as a where a.aco = r.aco ) as Sold_Bandwidth
from dslamdata as r where rbu = ?
group by aco
 

 The Last in the display when you would click on the +/- of the second gridview
 select dslamname,
(select count(secode) from dslamdata as a where a.dslamname = r.dslamname ) as Capacity,
(select count(secode) from dslamdata as a where a.dslamname = r.dslamname and dnum > '1') as Used,
(select count(secode) from dslamdata as a where a.dslamname = r.dslamname and dnum < '1') as Remaining,
(select (select count(secode) from dslamdata as a where a.dslamname = r.dslamname and dnum > '1')*100/(select count(secode) from dslamdata as a where a.dslamname = r.dslamname )) as Utilization,
(select sum(dwlink) from dslamdata as a where a.dslamname = r.dslamname ) as Sold_Bandwidth
from dslamdata as r where aco
group by dslamname
  
if you would look at it, all the codes are the same except for the selected field,
i hope someone can help me with this, thanks and good day
 
SALAMAT PO.,