Here is the letter I'm going to send to the service manager. The Isuzu Collective provided good advice earlier, I'm open to good advice now:
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Dear Rotten Bastards Who Stole My Tire
(just kidding)
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Service Manager
Chapman Chevrolet Isuzu
1717 E. Baseline Rd.
Tempe, Arizona 85283

Dear Service Manager

I have an issue I wanted to bring to your attention in case it is a repeating event.

A month ago, I took my 2004 Isuzu Rodeo in for servicing. This included rotating the tires. Last week, I left work early (I normally leave after dark; and it's the only time I approach my car from the rear), I noticed the rear didn't look right. It took me a minute to realize the spare tire was missing.

I checked the rear door for damage (it blocks the spare lowering mechanism)--none. The spare tire holding chain was rolled back up, and the extra chain was tucked up neatly. (i.e. it's not dangling down or I would have noticed it immediately).

I called your service department (Tuesday, August 14th) to ask if, during the power outage and resulting confusion, my tire was put aside and forgotten by mistake. I left a couple messages and my call wasn't returned; when I reached a person he replied he had called me, but didn't leave a message. That is possible.

I explained the issue and was told I'd be called back the next morning (Wednesday the 15th). When the call wasn't returned that day, I was on the phone Thursday morning. I learned that my tire wasn't found. I was disappointed that my calls were not returned, even to say, "I promised you I'd call, but we're still looking into it."

One of two things happened to my tire; either someone stole it off the street, or it was taken while being serviced at the dealership. Let's examine the probabilities:

Theft:
I drive my Rodeo pretty much just to work and back; even grocery shopping is on a military base. It would have to be a parking lot thief working out of my job or my driveway (rear end of the car facing the street) taking the time to remove the tire tire with the access door locked. He did this without damage, and instead of a quick getaway, took the time to neatly clean up his work afterwards, rolling up the chain and tucking away the extra.

Even if I left the doors unlocked, he either used his own tools (including the odd-fitting rod to lower the tire), or took the time to get mine out, use them, clean them, then neatly return them to their holding space under the rear seat, and then put the seats back in place. Despite full access to the Rodeo, this very neat thief didn't want to steal my iPod/accessories in the glove box (ok, it's just a 1 gig, but it's a target), or any of the change I leave in my cup holder or ashtray. A very honest thief.

Dealership:
I called Wednesday and booked an appointment at the dealership, first one on Friday morning. When I arrived, the service department hadn't heard of me. I had the number in my cell phone and GPS, I called the correct number. While working on my car, the power went out at the dealership. This caused confusion. My car was worked on, including a tire rotation. I do not know if 5-tire rotations are standard, but the four tires I have have both before and after noticing the missing spare are roughed up from 4-wheeling; the spare was pristine. I paid by credit card (I left a signed, blank template so you could fill in the amount later as I didn't want to wait for power to come back up before I could leave). I returned the next day to retrieve a receipt (for warranty proof) that had several minor typos in it.

I do not have any proof, and didn't spot it soon enough, to say for certain it happened at the dealership. However:

- It is very suspicious. I do not hold the dealership responsible, however you might have a dishonest mechanic that either made a mistake and covered it up, or has done this in the past to sell extra wheels and tires on the side.

- Not being able to reach a person, not getting calls returned from voicemails, or not receiving promised return calls when a customer is looking for a wheel/tire combination I'm rough-estimating at $350, was frustrating. A few minutes of communication leads to a much happier customer, no matter what the issue.

- The small errors, normally ignored, because annoying. Lost appointment, receipt with saying it was 6k service on a 2003 Rodeo with the wrong address (I'll give you the address), instead of 15k service on a 2004 rodeo and the correct address.

Again, I have no proof, and I do allow there's reasonable chance it was a roadside thief and not your dealership. I will probably stop by again the next time I'm in town to get my Rodeo serviced. I hope this is a one-time event, and I'm the first (and last) customer who brings this issue to your attention.

Respectfully,
Me