Poor Suction

[Crasey65]

We have recently opened our above-ground pool for the season and have replaced a bad multi-port valve seat and filter sand. The pump and filter are working great. However, when I hooked up the vacuum it loses suction within a minute or two. It doesn't seem to have enough suction to pick up the smallest leaf let alone the minute particles of debris on the pool floor.
I've removed, flushed out, and replaced all the hoses, and even bought a new vacuum head, but still not much suction.
The only thing that I have noticed is the hose connecting the skimmer to the pump leaks just a bit, but it did do that last season without problems.
What could the problem be and how could I resolve it?
Thanks.