Foreign Extra Stout Too Sweet

A while back I brewed a foreign extra that has a sweetness I'd like to tone down. I lost the recipe in The Great Hard Drive Crash of 2011, but the ingredients are as follows.

5.5 gal batch
2 row 13#
Black Barley 2#
Flaked Barley 1#
Carapils 8oz.

Mashed around 152/153

I believe this was the hop schedule.
Cascade 1.5 oz. 60 min
Challenger 2 oz. 60 min

Wyeast American Ale 1056 (puzzled by this choice).
OG 1.078 FG 1.017 (I hit these +/- .001)

I'm going off the order history for the ingredients and what I remember from that day. The beer turned out awesome and is an arse kicker, but It took half the keg for me to put my finger on what was off. Would the Carapils be the culprit, or just plain old mashing too high? I'm getting ready to try this one again but don't want to change too much at once. Would mashing around 151 or removing the Carapils have a more drastic effect?
This was my second all grain btw. I know some downplay the difference in extract and all grain, but I saw a huge jump in quality going ag. Thanks for reading.

use a yeast with better attenuation, maybe Nottingham or s04? You could swap the carapils for wheat malt as well.

Well if my calculations are right you got about 78% attenuation which is good in my book. I was under the impression that carapils does pretty much the same thing as flaked barley adding body and head retention but I think it does also add sweetness.

I think I would just ditch the carapils mash at the same temp and see how it goes. I think if your FG is any lower it is going to become to thin.

I am an all grain newb so take what I say with a grain of salt.

I have used WAY MORE than 8 oz. of CaraPils and still not have the beer come out sweet.

I say high mash temps are to blame

I would do both. Lower the mash temp to 150 and cut the carapils in half.

What temp did it ferment at? I don't really see any reason for it to be sweet. Have you ever had an Imperial Stout? Serious question, just thinking it may seem sweet to someone who isn't familiar with bigger stouts. My FES usually finishes around 1.018-1.020 with a similar OG. I typically mash at 154. Sometimes warm fermentation gives off esters, making it seem sweeter than it is. Just a thought. Other than that I don't know, unless your hydrometer is off or something.

Fermented around 70F. I have a chest freezer to control ferm temps now. I may go with the combination of half the Carapils/lower mash temp. Thanks for the replies.