That is one powerful pump! At 40' of head it flows over 100gpm! To get it down to 40gpm you have to have over 70' of Total Head.

Can you bypass the filter so the pump runs from skimmer to returns? If you can do that, does the flow improve drastically? Does the pump cool down?

You have a small, little filter with a super-powerful pump designed to roof solar panels, fountains and waterfalls. I'm no pump expert but you have 'WAY too much pump!

I wonder what the installer was thinking, with only one skimmer and no low drain. It's clear: Your pump is over-heating because it can't flow enough water--too restrictive.

What to do? Here I'm just making WAGs...Wild A-- Guess. IF it works OK when you bypass the filter and the pump cools down it could be as simple as just getting a bigger filter--one that handles over 100 to 120 gpm. If you like DE, they make them that big and bigger.

If it doesn't then down-sizing the pump is probably better. Something like a 3/4-1 hp uprated pump or a 3/4 full-rated might do it, but sizing has to be done correctly.

There's a very good chance your DE filter has been damaged. It should be opened and examined if you are going to keep it.

These are just starting ideas. The real pump guys can guide you better than I can.

There are ways to calculate and to estimate total feet of head, but I don't really understand them.

Carl