Clydesdales/Athenas (200+ lb / 91+ kg) - Unexpected cross-train pain

I'm doing more cross training to get myself back into shape after a bit of a rebound (back up to 250 from 235 in mid-summer.) I've always been a hiker and even when I can't get out to the mountain trails, I still take my dog out for an evening walk of a few miles on the neighbourhood trails... but those trails are all flat.
I started up a step routine this weekend, and my calves are just screaming. Even after a 4 mile uphill hike I've never noticed this level of soreness. Anyone else ever surprise themselves with what ends up sore after starting a new workout routine?

I once hiked a hillier than I was use to trail and I managed to tear my calf muscle. My errors were I didn't stretch once I started to feel my calf tightening up on the hike, and I didn't stretch when I was home and resting. I had a series of painful muscle spasms that night and during one of them it was so painful I kicked my leg out and tore the muscle nice and deep. It took 3 months to stop limping and another 3 months before it was healed, and I have to be careful after I exercise because it'll be really sore.

I've added a step routine to my workout but I concentrate more on using my quads rather than using my calves (foot flat on step, not toe on step). I'll do a handful to strengthen my calves but I'm a total sissy about it.

I once hiked a hillier than I was use to trail and I managed to tear my calf muscle. My errors were I didn't stretch once I started to feel my calf tightening up on the hike, and I didn't stretch when I was home and resting. I had a series of painful muscle spasms that night and during one of them it was so painful I kicked my leg out and tore the muscle nice and deep. It took 3 months to stop limping and another 3 months before it was healed, and I have to be careful after I exercise because it'll be really sore.

I've added a step routine to my workout but I concentrate more on using my quads rather than using my calves (foot flat on step, not toe on step). I'll do a handful to strengthen my calves but I'm a total sissy about it.

I know I didn't tear anything, but the muscles are pretty tight right now. I did some extra stretching before and after the ride to work, and I took the "flat" route to get here.
I hadn't thought much about technique for a step routine, but if I think about it, I was definitely not putting my whole foot flat on the stair. I had the front half of my foot on the stair, similar to how I would climb a flight of steps.
I'll keep up with the stretching, watch my technique on the step routine, and probably keep up with some Mineral Ice in the evenings.

I would suggest a couple of ibuprofin to help with the pain.