The difference between plugin and ajax in communication way with QlikView Server. Ajax works through web server and plugin connects directly to QlikView Server by qvp protocol.
Do you have tables that visualize 1M+ rows? Try to limit visible number of rows by calculation conditions.
Move web server on separate machine.
Use IIS web server instead of QlikView Web Server.
BTW, what is your server configuration hardware and software?
I am also facing same issue, I am having just 500 MB QVW but one dimension has 2,13,523 distinct values. Chart is not loading when am using this dimension. All other dimension with less values are loading properly.
This dimension is loading fine from access point but not from Ajax chrome UI. Please let me know any suggestions to improve the performance to load from UI.