I'm in the same boat with an over-sized pump. Last year with a complete refill of pool water, it took a month for the pressure gauge to register any increase. At first I thought "hey, it's fresh water--there's nothing in it. Then I found this forum late July last year when I started looking for info because of algae problems. I began to think that the stem coming from the laterals into the 5 way valve wasn't a tight enough fit and that the path of least resistance was there rather than through the sand.

Long story short, I learned about CYA (mine was in the 90's) and solved the algae problems. Tried the DE trick and even though I noticed some DE on the surface of the pool, pressure would increase at a faster rate as time went on. In other words, the filter was now acting like a filter. Without the DE, I think I could have gone that whole season with only about an 8 lb increase.

That little trick and the "Best Guess CYA chart" have solved 98% of my problems. The other 2% are self-inflicted. My water has never looked so good. Maybe it did one time back in the late 80's but it only lasted for 5 minutes. I can now live with this oversized pump till it dies or I get a VFD for it.