The other replies to your search are correct: the copycat recipes on the web for Pizza Hut's Creamy Italian dressing don't even more close to being poor imitations.

Like you, we're desperate to find it and we've experimented with some variations. Here's what we have found. We're getting closer, but still not quite there.

First, it tastes to us like a combination of Ranch dressing and regular Italian dressing (Wishbone or whatever).

So we started with a base of either Ranch dressing or a combination of 1 part mayonnaise and 1 part sour cream with some dry Ranch dressing mix added. Then we added about 1/2 part vinegar, a touch of lemon juice, and some garlic powder and onion powder. Also added 1/3 part vegetable oil and some finely grated carrots and raddishes.

We're experimenting with a drop or two of Worcesteshire and a little pickle relish. We're still looking for what it is that gives it the tangy flavor without making it sour. Haven't quite found it. Would be interested in whatever anyone else finds.