Thanks everyone for all your input. If I've learned anything from this, its that there really really could be several explanations to the failures. I understand what someone said above, that changing too many things at once might not ever reveal exactly what is failing.....but I can't afford the time to just adjust each possible culprit with each batch. I'm going for all my weakest practices and changing them all just to get some confidence back.
My bottling process is pretty standard. Clean with Easy Clean. Sanitize with Idophor. Rinse everything. Transfer from fermenter into clean/sanitized bottling bucket. Siphon and fill bottles with racking cane. I can't remember if I boiled the caps last time or not. I'm pretty sure I did. I'm using the caps that come with brewer's best on some bottles bought at the local shop and some recycled.
I don't think it's the caps anymore since, yeah, there is a head on the beer.
I'm suspicious that the very faint stains left on the carboy...that I can't get at with my brush...might be a problem.
Overall I might be too impatient in cleaning my gear overall.
I'm concerned about the fluctuations in temperature in my drafty house. This fall the basement's temp has fluctuated within 10 degrees in the two weeks I've gone from primary to secondary.
I'm going to get some new tubing and do my best with the bottles.
The thing is, I'm so excited about this batch that I know I want to keep trying anyway. What is intimidating is the cost of the BB extract kits. I wouldn't feel so bad messing up batches if it was cheaper. So now I'm trying to decide with my wife if I'll spend the money to put together a mash tun and go to the next stage. I understand I can get ingredient costs down substantially after those initial costs. Plus I have a really good friend who wants to get in on this. It'll be time well spent with him.
Thanks for your help!