my feeling - after installing OpenACS and dotLRN more than a dozen time is that the problem is from OpenACS itself.
So one suggestion! Just to make sure that I am wrong! Please install on the same box a clean instance of OpenACS on another port using the same files on the machine but a new database service1 without any users batch synch'ed.
If I am right this instance will run very fast as lightning. And if it does there was a misconfiguration with the OpenACS params. Soplease post your kernel, main site and authorities params for a quick check (maybe you can simply make screenshots to save you time).