Weak at the 5k compared to 1500 and 10k and up

You probably have good leg speed (1500) and endurance (10km and up) relative to your VO2max. You need to do more track workouts at 3000m/5000m race pace. Something like 5 X 1000m with equal rest.

The 5000 is a tough event. I always liked the 1500 cause while it was fast running and brought on a lot of oxygen debt it was over in 4min. You could always stand the pain for 4 min. However a 5k is a lot of pain for about 10-12min. Once the first km was out of the way it started to hurt and by 3km you knew you were in the weeds.

And the training for 10km and up is relatively easy: tempo runs, mileage, 10km race pace work and some MaxVO2 work. Training for a good 5km means a lot of MaxVO2 work and some running faster than that. Intense running with little rest. Painful like the race. Rest assured though if you do the right training the racing is a little easier.

Try 7 x 800 at just under 5K pace with decreasing rest:

(2:00 after first 800 rep, then 1:50. 1:40, 1:30, 1:20, 1:10, 1:00 on each subsequent rest).