McClary (GE) dishwasher not filling pro...

I have a McClary dishwasher that is doing a poor job cleaning the dishes.i have been playing around with it a bit and have noticed the water level is never as high as it should be.I checked the switch that controls the level and it is clean and working properly.It seems like the timer closes the fill valve before the level switch has a chance to.could this be caused by poor water pressure or possibly a partially plugged inlet valve.I have been dumping water in to compensate after it fills and it does a better job.the other problem is 5 minutes after it starts a cycle it wiil start to sound funny and the water level will be to low.the solenoid for the drain valve is not coming on during this time.i took the unit off that contains the plastic flapper with the rubber gasket on it that the solenoid operates.it appears clean and i could not blow air back through it but where else could the water go?any help would be appreciated.thankyou