[troy@uk]

  I bottle condition all of my beers. It generally takes about 2 weeks to finish @ 68 - 72 degrees.  Lately (the last five batches) it has taken closer to a month.  I use beer smith software and use corn sugar or DME depending on the style.
  Obviously I need to look at what changed.  I wish I could remember where on the WWW I read about not clamping down the caps right away.  The idea was to place a crown cap on the bottle loosly and that the priming sugar and yeast would start working right away and create CO2 which would drive the lighter O2 out of the bottle before you crimp it down.  This sounded like a good way to reduce ozygynation, and I could work alone and take my time so more O2 gets out.  After all of the bottles are full, I start crimping, so we're only talking about 30-35 minutes.
  Does anyone think I could be loosing that much CO2 in such a short time?  I now have some O2 absorbing caps, so I will try going back to capping right away and see how that does.  (I'm still trying to interprite the proper sanitation method for these caps based on the thread on this subject.)

[BrewArk]

The time you are taking to cap isn't the issue.  It is more likely fermentation temperature & how long you are in secondary that is affecting the yeast activity in the bottle.  The better you can control your fermentation temperature the more consistent you'll be between batches.  If you've increased the amount of time you are in secondary that could leave you with less yeast activity too.

[tschmidlin]

I agree, if it were the time it takes you to cap them you'd expect the last bottles filled to have higher carbonation than the first bottles filled, since capping goes much faster than filling.

I would look at something else in your procedure - longer time settling before bottling, different yeast strain the flocculates better, different racking cane that doesn't pull up as much from the bottom, etc.  You can intentionally pull some yeast off the bottom of the carboy when you rack to your bottling bucket or add some fresh yeast at bottling, and see if that helps.

[Malticulous]

Taking a month at those temps seems odd to me, but don't be afraid to bottle condition a little warmer. If I think my yeast is not healthy enough I sprinkle in a gram or so of dry yeast as it racks to the bottling bucket and mix it in well trying not to oxygenate it. At 75F it seldom takes more than a week to reach anticipated carbonation. Fresh dry yeast is always going to be more healthy than yeast from the trub. It doesn't take much yeast, but healthy yeast do make a big difference in the amount of time it takes.

[tschmidlin]

If I think my yeast is not healthy enough I sprinkle in a gram or so of dry yeast as it racks to the bottling bucket and mix it in well trying to to oxygenate it.

Maybe I'm misunderstanding your procedure, but do not oxygenate fermented beer or you're just asking for staling problems.  When you boil water to dissolve your priming sugar, before you add the sugar carefully scoop a little water into a separate sanitized container to cool off.  When it's cool, rehydrate your yeast in that.  Depending on the OG of your priming mixture, you might not want to add the rehydrated yeast directly to that, but shortly after you've started racking then adding both to the beer should be fine.

[Malticulous]

The first 'to' is a typo. It will read 'not' when I edit it.  

Thanks for pointing that out. I'll try to to do better.