If you read just a few pages of posts in this forum, you'll see that virtually everyone reports the same experience: Kaplan scores being well below GMATPrep and actual GMAT scores. Kaplan is much harder, the questions are not very reflective of the real test, and the scoring algorithm isn't very accurate.
The best ones are GMATPrep and Princeton Review. Do those instead of Kaplan, even if you uninstall and reinstall GMATPrep. You'll get mostly new questions if you do that. I don't know if that works for the PR tests too, but you could try it.