Wife is too sensitive when I go down on her

Need some advice on this one... Whenever I go down on my wife she's always way too sensitive in that area. It doesn't matter if I've already warmed her up so to speak. Any ideas? I've read books and just can't seem to get past this sensitivity issue.

What do you mean when you say you've "already warmed her up"?
If she is already aroused, of course she's going to be more sensitive.
In my experience, while many women enjoy cunniligus......after a while, they become so sensitive than if you to continue for too long (this varies from woman to woman)...., that, for some, it actually starts to become unpleasant.
Let her guide you to what rings her bell and what doesn't......

Maybe your technique is too aggressive. Try using the flat part of your tongue and lazily exploring her entire vulva instead of just zeroing in on her clit.

Barbwire a.k.a. Cowboy Lover

When I say "warmed her up" I meant that I just don't go straight from pulling her pants down to going to town on her pussy. And when I do make my way down I usually don't start with the clit right away. The issue is that it "tickles" my wife anywhere in that region, even her inner thighs or the area around her pussy. I don't know I'm just being too easy or what

Is she able to use her fingers or a vibe to get off with?

Barbwire a.k.a. Cowboy Lover

She masturbates with her hands but I haven't been able to get her to try sex toys. Still working on that one.

Hmm, ticklish--yeah I can picture that. I think hands would help. Like if she has her hands down there at the same time so it would feel familiar and she'd feel in control.

Some girls just tend to be more sensitive, I had a girlfriend that any little touch would almost be too much for her, but the same technique with other girls I've found to be quite successful. Try not to focus all of your attention on the clit explore the entire region and try being gentle don't be too aggressive.