Hi Darryl,
WeBWorK will do most of what you describe for the quiz component of your goal currently. See http://webwork.maa.org/wiki/Gateway_Tests_and_Quizzes for a discussion of the gateway/quiz assignment. Gateway/quiz assignments are timed, allow multiple attempts, allow problems to be drawn from testbanks, and can allow students to see their work after completion.
Your tutorial sounds as if it could be minimally implemented by having a bank of tutorial homework sets students could work (we do this in one case by having the sets available in a course with a lot of guest users, in that we aren't concerned about seeing students' work). WeBWorK does not currently allow a set to have a length determined by students' success on it, but this is on the drawing board and may show up sometime in the next year.
Does that help with your project?
Gavin
Installation
Advice about a new installation for a tutorial/quiz system
This forum has a limit to the number of forum postings you can make in a given time period - this is currently set at 5 posting(s) in 1 day