DCA-LGA is operated by E170s now (not 175s). JFK gets the 175s. But both cities only have a few flights a day - I think 3x to JFK and about 6 or 7x to LGA depending on the day.
There is no signage in DCA about it being a shuttle any longer. I just took DCA-JFK a couple of days ago so my experience is recent.
-RM