Sounds like you still have some frozen lines. When I first started my pump day's ago it was only reading 18 inches. The kids and I walked the woods looking for big noisy leaks. We found a dozen trees untapped and a saddle that slide down a mainline about one inch due to a tree hitting last fall. After all the fixes the vacuum only went up to 20 and I was getting concerned. About three hours later I went back to check the gauge and I was 27-28. Have you checked your check valves on your releaser? Why do you have them? They could have ice in them.

Spud