Is my fermenation stuck?

I brewed up a brown ale last Friday and it seemed to get going and fermenting very quickly. By Monday the air lock has slowed to releasing a bubble about once every 40 seconds and it was down from the OG of 1.054 to 1.024. I checked it again today and it is still at 1.024. It seems to me that even though it didn't change the gravity is still a little higher than it should be. Here is my grain bill:

9.5lbs Pale Malt
1lb Toasted Malt (toasted at 350F for 10 mins)
0.5lb Dark Toasted Malt (toasted at 350F for 30 mins)
0.5lb Chocolate Malt.

I used reconstituted dry Windsor yeast and it seemed to get the brew going pretty quickly after pitching it. Is there maybe something about toasted malt or the chocolate malt that gives it a higher finishing gravity? I think it may have gotten a little cold because I was gone over the weekend without the heat on and it got relatively cold outside and the fermenter is about 55F now. I'm just wondering if it sounds like my fermentation is stuck and what I should do about it if it is? Should I repitch some more yeast?

If your fermenter is at 55F, let that bad boy warm up, ale yeasts start to go dormant around 60F.
Allow it to warm, and give it a gentle swirl to get the yeast back into suspension, if that doesn't work yeast energizer/nutrient would be the next thing to try.

If all else fails pitch more yeast, but 55F is too cold for ale yeast.

Sounds like your temps fell too low.

yea i gotta agree with shnitzengiggle let it warm up and see what happens. if it cold stalled then once it hits 60s it should start up again. ill agree nutrient cant hurt

Ok thanks for the info, I knew that a temp in the upper 60's was best but I didn't realize it would go dormant when it got below 60F. I swirled the carboy and have it sitting in my bathtub filled with 68F water to get it back up to a decent temp for fermentation. I think I have some yeast nutrient also so I will try that too.

Hmm the yeast nutrient I have is diammonium phosphate which says its for wines and meads so I'm not sure if I want to add it to my beer, also is it possible that adding it could contaminate the beer? I tried heating some up with a little water to sanitize and it started smelling like ammonia and I definitely did not want to add that to my beer. I'm a little skeptical of this stuff. Maybe I will just try getting it back up to the right temp first and if it still doesn't do anything I'll go get some other nutrient.

I think its working, I swirled the carboy and heated it up to 67F about 3 hours ago and the airlock has gone from 40 seconds between bubbles to about 10 seconds between bubbles.

yay beer. i wouldnt judge by airlock personally but it sounds like youre good to go

I normally check the yeast mfg websites to see what the optimum fermentation range is for that particular yeast strain, and I normally try to keep it towards the lower end of the recommended fermentation temps.

The exception would be belgian beers, I start on the low end of the optimum fermentation range, and let the fermentation free rise to around +/-78F