*sigh* After screwing around on the 'net, sounds like you're probably right. It's the "Deco" portion of AN/Deco that they have an issue with...
Dori Fish, what do you think about going diving sometime? I have no idea where you live, but if it's anywhere close to the Panhandle, we could probably meet up at Vortex and go for a dive or two. I dive a tech rig, and I'm certified to the AN/Deco and Apprentice Cave level...while I'm no where as skilled or as experienced as I want to be, it might be beneficial to you to see what is going to be expected of you when you start tech classes. I could show you what your buoyancy and trim needs to look like, and we could work on that some.
If this helps, I knew I wanted to dive caves after only a handful of OW dives...I think that my desire to become cave certified started at around dive 7 or 8. I immediately traded my BC for a backplate/wing and a primary/bungeed backup regulator set. Then, I hooked up with a very gracious tech diver, and we spent dive after dive just working on things like holding horizontal safety stops, shooting lift bags, frog kicking, and all that good stuff (we had lots of fun, too!). I didn't take Basic Nitrox until around dive 50, and Advanced Nitrox/Deco until around dive 100 (and I still felt like I was just barely ready for the AN/Deco class!).
It might be a wonderful idea to just stick with an Intro to Tech class, then spend fifty or a hundred dives or so working on those basic skills. No need to rush for those certification cards...they don't do anything except fill your wallet if you don't have the skills/experience to back them up.