Update:
I haven't kegged the amber yet. I will probably do it this weekend. I have been really busy and having a ****ty week to boot - (minor car accident that was 100% my fault, screwed up a config file at work that made me waste 16 straight hours of time, and in the cleanup of that, accidentally blew up the customer's production server) so I haven't really had much time, except for the fact that I was able to squeeze in a brew session on Monday.
I got my pH meter, and I also watched John Kimmch's Q&A video on youtube (which is EXCELLENT, btw), specifically the part about mash pH. I wanted to shoot for 5.2 on Monday, and I used Bru 'n' Water to figure out the acid additions I needed to make. I followed everything to the letter and the mash pH came out to 4.8 at room temperature.

So it's apparent that I will need to adjust mash pH on the fly next time.
This is the recipe I brewed:
http://wiki.homebrewersassociation.org/LaraPaleAleNHC2009
With one change... I like my beers a little darker, so I added 6 oz of special roast to "orange" it up a bit. Other than that, exactly as brewed, adjusted to 5 gallons and the AA% of the hops I have on hand. I plan on kegging this within the next week and I will try to hold to that. My efficiency was 86.4% this time around, even with the 0.042 gap in the mill.
The bottled and kegged Tangerine ale: They really are two completely different beers. The bottled ones have carbonated up pretty well by now, and they taste quite good. There is a good tangerine flavor in the beer. SWMBO smelled and tasted it and recognized the fruit flavor in it right away. Her sense of smell and taste are better than mine.
However, out of the keg, it's nowhere near as good. The "off-flavor" has settled a bit and doesn't jump out of the glass at you. But it's still not a very good beer. There is enough of an off-flavor that really ruins the flavor and aroma of the beer. I have been making myself drink them, and they're drinkable, but not very good.
In the meantime, I swapped CO2 cylinders again at the welding supply shop. I also got a chance to speak to the manager. It turns out they deal a LOT with local wineries and breweries - this is wine country, after all, and Sacramento has an exploding craft brew scene. He said that I am the first person to suspect anything wrong with the gas. No one else has reported any problems. So take that for what it's worth.
I plan on brewing next Monday again. If Bru 'n' Water models my mash pH at 5.6 I am going to see if that will end up at 5.2.
Is it possible this whole thing is astringency from too much alkalinity in the mash combined with carbonic acid from force carbing the beer with CO2?