Had the same experience when I started working on my running form a couple years ago. My hr was going almost 20bpm higher, yet I was running 1 min per mile slower than before. Give it time– takes the neurologic system some time to adapt to new movement patterns. I also had a lot of calf tightness, but that went a way (mostly) through time and rolling. Just be gradual in your changes and I’m sure it’ll be fine.