Are Theists Illogical for Believing in God?

[Autumnlicious]

I.e.
1) Data from nature
2) Data from revelation
Both require reason to understand, so revelation cannot be opposed to reason.

Your conclusion does not follow at all. Reason is required to understand anything, including the ravings of a lunatic. That doesn't negate the fact that the ravings are illogical.

but a lunatic can be logical even if its conclusions aren't true.

Or a lunatic can be absolutely logical and correct for some things but not all things.