Auto complete Extender very slow at firstload.. ?

You are the same person asking about the "Page level cache" problem too, aren't you? :) Anyway, in this case it really depends on how much data you are loading in your auto-complete extender and whether or not the data is coming from just one table or its being joined with several other tables and then returned. And the reason it takes only 0.5-1 secs second time on, is that it caches previously loaded results and uses them if you type in the same query string again (i.e. if you set the caching property to true). Have a look at your DB queries and the query execution plan. Optimisation problems are very specific to the system architecture and overall design, so it is difficult to come up with a general remedy.