OK, so your 3 way is open all the way. But there are ALMOST always cutout valves on the solar, there will be one on the pressure side and one on the return side. You need to check those. They will most likely be at the pool machinery, but I have seen pictures where the valves are on the piping going up the house. Most of the time these are left open when you winterize, but they could have been shut.

Come to think of it, you may actually have 2 sets of cutoffs, one set near the pump and one on the house piping.

Anyway, THOSE valves need to be open. If those valves are open, then you probably have a pipe blockage. I would think if you pump had given it up, you wouldn't have the steep pressure gain.

Take a picture of your solar piping/valves (include the 3 way and a good area around it) and attach it so we can get a look.