Lower leg injuries in classic skiing

For the past year I've been battling a recurrent problem -- pulled
soleus/gastrocnemius muscles -- in my lower leg. The problem is
associated only with classic XC; skating doesn't bother or trigger the
problem, probably because it involves a push to the side rather than a
kick back along the axis of the leg. In any case, I had to give up
classic skiing entirely last January.

Thinking that the problem was due to insufficient strength, I spent a
lot of time running, ski striding, hiking, climbing, and biking during
the off season, and I was optimistic going into this season on snow.
But the first time that I tried to put the pedal to the metal the same
injury came back -- worse than ever.

My physiotherapist recommended that I see a foot specialist. I have
used custom orthotics for years, so I thought that I had addressed
that issue, but with nothing to lose, I went to see Terry Makos, the
boot fitter here in Canmore. He said that he's seen a rash of injuries
identical to mine in the last year -- all associated with classic XC
skiing. He has solved many of these problems by inserting heel lifts
into the boots, which effectively shortens the soleus/gastroc muscles.
We tried it an initially things went well. But when I tried a long,
easy ski the other day the injury came right back (I was limping the
next day). Terry and I are still trying to find a solution (more heel
lift), but if we are unsuccessful I'll just have to give up classic
and go with what works -- skating. I mentioned my problem to a friend
who gave up classic skiing a few years back (he only skates now); he
said that he also had similar trouble with classic sking and tried a
heel lift, but that the resulting forward lean of the body caused the
skis to plow, i.e., they didn't glide as well when double poling. I'm
willing to give up a bit of glide if I can just classic without
injury.

My questions for the group a Has anyone else seen this problem? Is
it associated exclusively with classic technique? What solutions
worked to resolve it? Is the glide penalty associated with a heel lift
real?

P.S. My classic boots are Salomon Carbon Pro Classics, but the problem
came on when skiing in my previous bright yellow Salomons, so I don't
think it's an issue with the new boot.

-Everett