I too have been in that boat, if light years slower than the D1 level. But I've been running for 25 years and I've been around some good coaches.
What I've seen work is really two sides of the same coin:
1) go slower than you can bear in interval workouts for 2-3 weeks. Maybe use the McMillan calculator and force yourself to run 1 sec per 400m slower than the slowest pace in the range it suggests.
2) Channel 100% of your aggression to your next race. Stop with this delayed gratification business. Next race, treat it like a conference championship.
The idea here is to force yourself onto the next plateau by shock therapy. By going almost easy in intervals, you will be bottling up your competitive fire - you'll want to get out and fly in a race. We would be working on your mental edge here - trying to bottle up all your physical and mental energy and let it go ONLY in races.
The other thing may be to change races for a meet or two. If you are a 1500/5k guy, try a 400/800 double or even a 10k. or a 400/5k double. Doesn't really matter - the point would be to make you feel like a kid again, rediscovering the challenge of racing, rather than just grinding out another 1500 when you have done 300 of them in your life.
All this is aimed at rejuvenating your mental state - If you are doing the training you say you are at the D1 level, you are fit - the key is getting the mental fires burning very very hot.