draft issues please help

I have a harman accentra freestanding ... i believe i am having draft issues... my stove goes into a tee up a foot into 90 then staright 2 1/5 feet the horinzonatl run is straight does not angle up would it be better if i add 90 and go up 4 ft after the straight run???

see the post in the YELLOW sticky post at the top of the pellet and corn room
and more links here
http://www.hearth.com/econtent/index.php/forums/viewthread/13422/

and here
http://www.hearth.com/econtent/index.php/articles/installing_pelletstove

yes i have cleaned it lately and the links i already knew about
i wanted to know if it would draft better if i added more pipe

Yes it would

The reason I gave the links were some of the articals in the links explains the venting
and sometimes it could be from air leaks from ash pans and doors or blockage in the Ash trap passages.

thank you for your help i did check all my gaskets and i have cleaned the stove many times because it was black soot building up
even after cleaning it back to back thats why i thought it was my draft
the 90 then going horizontal for almost 3 ft got me worried
thanks agian