You sound like a clone of my younger self. When I was in my late 20's in my second or third year of consistent running & racing, for some reason I was slower in 5K than 5 - 10 miles.
My advice is to just keep doing what you're doing. Don't blast shorter intervals! Just keep focusing on consistency and getting your mileage up. Repeats ranging from 400 to 1600 are the way to go. Eventually your 5K ability will catch up. The one thing that I think helped me in addition to the mileage is to run the occasional 3200/2 mile time trial. Not necessarily all out, but keep it hard.