Repeating what other knowledgeable runners have said. Drills, hills, accels/flys, and lifting should do the trick. Don’t recommend “real plyos” unless racing 100-400m. Yoga classes can get expensive and the ROI isn’t great unless you’re there for the eye candy.
I’ve suffered from the “shuffles” from time to time. Mostly it’s due to being out of aerobic shape or not doing enough ancillary work.
Last outdoor season as a 43 yo I ran low 58 400m (after an earlier 3K) in the beginning of the season and a 4:29 1500m later on (both FAT).
Drills 2x a week: A skip, B skip, C skip, Cariocas, side shuffle, butt kickers, high knees, fast skip, high skip, long skip. Most distance runners have weak and tight hip flexors and lower legs. These will strengthen and improve range of motion. The shuffling comes from not being able to lift the legs or push off the ground quickly. Most of the drills involve hopping and reducing ground contact time. For many runners the longer the foot is on the ground, the more pronounced the shuffling. When possible, do drills barefooted on a soft surface. Again build up to barefoot drills by starting out doing only a few barefoot and the rest with shoes.
Lifting 1-2x a week: Kettle bell swings, lunges, and step ups. Squats alone tend to tighten hip flexors. Lunges and step ups will help with leg balance and drive. Start with just a few and add a 1-2 reps each week. Many shufflers, regardless of age, run hunched over and/or roll their shoulders in. Strengthen the back with two or three of the following: pull downs, military press, pull ups, rows, back extensions, planks, and Superman’s.
Accels/Flys 1-2x a week: In the beginning start with 3 x 20-30m and incorporate leg drive (extension of trail leg + lift of front leg) . Hit around 80 percent of max speed . If you’re doing it right, your hips will start to fatigue near the end. Every few weeks add a rep and 5-10 more meters. After a few months of progression you can work up to flys, hitting and holding top speed.
Jumping rope in place is also an excellent exercise to strengthen lower legs and reduce ground contact time.
Best of luck out there.