If you have 19 after the pump it is not a pump issue; as you have established vac in the line. Things to consider:
blockage of the line from ice or other like debris.

If you had a bad tap then you should not have a good vac reading any where due to the air from the hollow spot would not allow a vac to be established in that short of a system.

If you had a long system then yes you could establish some vac with a major leak a long ways away. IE: I had a major Fup this season, my young crew plus a girl friend...major contributing factor as she is very cute. forgot to install a plug or valve in the end of a new main. The 1" opening was about 4000' from the vac pumps. I was only able to get my vac up to 18" with one pump so I thru a valve and started the backup pump and the two together I could pull 24" ??? the search was on. We found a hand full of leaking saddles and one spout that was cut in, hole drilled and the spout not installed...I blame that on a kissing break

Walked all the way back thinking I had found the issues and the vac was only up a little. So back out I go listening to every saddle and watching bubbles. They were so slow and the closer I got to the issue the louder the main was. I walked all the way to the spot of the missing plug twice. The tubing made no sound at all. I decided to check hose clamps for leaks and found the last one was missing as was the plug. Funny thing the plug for the job was not in the UTV any coats, or the sugar hose. They don't recall if they put it in or not, so I am on the look out for gremlins.

Check the obvious and the not so obvious. You could have an ice dam in the line caused by a leaking saddle that froze the sap flow in the tube. I saw my first one of those this season in my pyrex dry line in the sugar house. Just before a connection there was an odd ice formation that grew for an hour as the trees started to flow the first day. The sugar house was supper cold from the winter and the ice dam grew til it nearly plugged the 1.5" line. Just before it plugged it off the dam disappeared into the releaser. My cell was dead so I couldn't get a pic.

This will be a great learning experience for you...after you find the issue.

Good Luck on a speedy conclusion!

ben