which cable splitter is best for 4k on COX

My internet (500Mb down, 50 up) works fine, the tv signal tested fine until after a 3way splitter and it stops working several times a week for the 3 tvs, one new main box, two mini boxes.

3 service calls with new main box replacement, street connector redone, signal tests fine through the internet connection, and poor after a 3-way splitter to the 3 cox boxes.

Last service rep worked for 2 days, installing a signal amp before the three way splitter, but signal still drops off the mini boxes and the main box at unpredictable times. Resetting the boxes by unplugging the power supply to force a reboot takes a long time to sometimes get a tv working.

I suspect that the 3way splitter or the cable connection after the internet signal splitter is bad.

I need to know what the specification should be for replacement 2-way and 3way splitter should be.

This bad signal strength seems to be related to the extreme heat we are experiencing  for the last couple of years. The house attic is over 100F, even with about half of the roof covered by solar panels.

The repair service seems to be dead to new phone calls!