I have a 1.5 hp Hayward Tristar pump that I run constantly on low speed. When the filter is clean, it reads 0 psi on low speed, 20 psi on high. If the psi rises to 5 on low, it barely pushes enough water through the jets to notice it on the surface of the water. Meanwhile, if I switch it to high, the PSI is about 25 and the water flow is fine.
Are you supposed to backwash DE filters earlier than normal (i.e. less than a 10 psi increase) if you use the low speed setting?