Hard start

Have replaced distributor, plugs, plug wires, battery, fuel filters. Fuel pressure checked out correct. Still have to crank engine repeatedly. Sometimes fifteen or more "cranks". When key is turned fuel pump engages each time but then tone of "whine"will change (very subtle) will then start on next attempt. Runs fine after finally get started but sometimes will start better rest of the day sometimes have to go through all of the above each time it starts. Think it is the fuel pump even though the pressure checked out?