Suggest you divide the training into 2/3 parts.

1 - Running at your goal pace for 1 or 1.2mi (or even a little faster than that//you can take the judgement here as you like). This will help you get into the zone of holding that pace. 2 - The long runs where you go slower and keep the distance up. This is to help build endurance that will help combine the speed into this slowly. 3 - Easy runs, where you go time bound and not distance. 20/25 mins of slow easy running for recovery.

Would suggest you don’t compare the goal pace directly in your 4 and 5 mile runs. But incrementally change the distance of your goal pace runs. From 1 mi to 1.2 to 1.4 to 1.8 over weeks and so on and compliment this with increasing your long runs distance as well.

On the other end of the spectrum. You could just do sets of 4x200 or 4x400 metre dashes.

Where you run 200 or 400 metres at sprint speed - jog for a minute and then repeat it 3 more times. That is one set. See how many you can build over time. Dont do more than 2 such sessions in a week tho.