Decent endurance but lacking speed

Just like lifting, once existing muscle is tapped out for heavier load - you need more muscle.

Pushing your mass faster is a heavier load.

It is very difficult gaining more muscle in a diet, usually only going to happen during first few months of activity that is using the muscle, in other words you tap it out fast or you had very little to start with, and then within that first 6-9 months you increase the load (faster for running, heavier weights for lifting) and you slowly get more muscle.

Sadly after you've done the activity for awhile, it's hard if not impossible to gain more muscle in that diet. Endurance can keep increasing, as that's just about storing more glucose and using fat better as energy sources.

But you can try.

The cardio activity that is as close to lifting as you'll get is HIIT.
And not the fad activities that HIIT name has been slapped on - true HIIT.

Now, before the HIIT routine, the other potential issue is whatever pace you have been doing for that hour to finally improve to 10 min/mile, could be full out effort, as hard as you can go.
If that has been the case, you have been training your upper aerobic carb-burning system, not your lower aerobic fat-burning system.
It's easier to tap our the upper range and not make much improvement, and it doesn't help the lower range much at all.
But if you can train the lower range, it also helps out the upper range.
And you can actually find the mantra true in endurance sports - "slow down to speed up".
Which means you train at the lower HR to train fat-burning system (which is also less stressful), and the pace starts picking up despite the HR staying low.

Do you use a HRM, or have any idea of what level your HR is at doing those 10 min/miles?
I'm guessing since you can't speed up, it's pretty high.

The other aspect could be form is just not good, being too inefficient, causing some issue with above point, and just wasting energy.

The fartleks are great to practice that faster form. You pick up the pace for that 2 min by just say 30 sec/mile, so 9:30/mile for 1 min, working up to 2 min.

The HIIT is a little different, it trains that upper ranges even more than running full out for 1 hr would do, but it also calls on the muscles to be overloaded, and when you allow rest and recover and eat enough - they get stronger and grow more if diet allows.

Here is 1 simple HIIT (High Intensity Interval Training) and SIT (Short Interval Training) routine that should only be done 1 x weekly, and rest day following, and light cardio day before, because you need to have the strength for this, not worn out - no benefit if attempting it already tired from prior day. This can NOT be done on treadmill. It is impossible to go all out for short time on treadmill. None change fast enough to allow the effect that is being desired.

5 min warm-up walk.
5 min warm-up jog slow.
2 min jog normal.
15 sec all out sprint as fast as you can go.
45 sec walk, last 5 sec start slow jog again so not sprinting from a walk.
Repeat Sprint/Walk 7 more times, so 8 x total.
20 min slow jog to recover.
1 min sprint to maintain pace/effort the same over the whole 1 minute. So not fast tapering off, but try to max out.
1 min walk.
Repeat 4 more times, so 5 x total.
5 min cool-down jog slow.
5 min cool-down walk.

That's 1 hr.

There are Timex Ironman watches with good interval routines function that work well. The 15/45 is preset. During first part of slow jog recovery while maybe walking, it is changed to 1/1 preset. Stopwatch used for other aspects.

And if you have 118 to lose to healthy weight, 10 min/mile is excellent, don't sell yourself short. Once initial improvements are made from exercise, it takes longer to keep improving. Again, even harder in a diet because recovery is impaired.