fluctuating water pressure in the kitchen sink

We have always had poor pressure in the kitchen sink. The city recently flushed the lines at which point the sink went to a trickle and water pressure will not fill the dishwasher (2 problems). Water pressure is fine in the rest of the house. Replaced both valves and faucet. Beautiful water pressure! Problem solved! Nooooooo! The good pressure lasted only 1 day, now it is down again (not to a trickle, but enough that the sprayer in the faucet will not stay engaged in the spray function. Please help! Our home is 10 years old.