These could be signs of a horse that is dragging an invisible ball and chain looped around the base of his neck. The weight of that invisible ball and chain is causing him to be heavy on his front end and feel the way I have just described.
I have ridden such a horse. It was very confusing experience because when Jody sped up and gaited she felt wonderful. Her shoulders were free and she reached out in front like she was supposed to. Then when I asked her to transition to a flat walk, she would slow down, stiffen her shoulders and shuffle her front feet along the ground. If I asked her to "dog walked" , she could keep a relaxed shoulder and reach out with her front feet quite nicely. But as soon as I asked her to move her walk past a dog walk she would automatically stiffen her shoulders and shuffle along, often tripping over slightly uneven ground. I tried stepping her over ground poles and it helped for just the moment she was stepping over the pole. As soon as she was over it she would go back to shuffling until the next pole.
I thought Jody should feel heavier on her front end because of her foot dragging but she really felt pretty good. I was truly scratching my head to figure out how to help this mare. I tried different approaches and finally after a lot of frustration for both Jody and myself, I realized Jody's chest was closing in on herself instead of broadening and opening up. When Jody sped up and gaited, she opened up her chest thus giving her shoulders and front legs the freedom they needed to move forward. When she came back to a flat foot walk, she automatically closed her chest and went back to stiff shoulders and shuffling front feet. Once again that invisible ball and chain turned into the heavy weight for her to drag along the ground. When I realized what was happening it became obvious that I had to open up her chest whenever she was walking. I took her to a sandy wash that was close by to start the process. In the wash she had to slightly elevate her front end in order to pull and push her way through the loose sand. It was a lot more work so it forced her to open up her chest in a natural way while she learned how to walk without shuffling. Walking over the poles had taught her to raise her feet to clear them, but the sandy wash with it's consistent deep ground helped her feel what she could do if she kept her chest open. The deep sand also forced her to work harder than walking over poles. I understand not everyone has access to deep sand. I know that a plowed field is similar to sand but it can be difficult to find a farmer who will let you ride in his fields.
Jody's ball and chain is getting smaller but because her muscle memory is used to a closed chest, it is taking time for her to shift to an open chest in order to allow a full striding walk.
I realize it might be difficult for someone to recognize if their horse has an open or closed chest. All I am intending to do is expand your thinking to the possibilities. Then it's up to you to decide whether your horse has an open or closed chest.