2000 malibu no start

Cranks but wont start, 50K on the odo. Replaced blocked fuel filter. Car will start and runs fine when started. When it doesn't start I have figured out that if I rock the car, fi about 2 minutes it will start. I use injector cleaner in the fuel and also water evaporator. Any clues would be helpful.

Have you checked the fuel pressure when the car won't start?
You will need to check that and for spark when the car will not start..this will lead you towards what system is causing the problem...once that is done, then you can determine if it is a control circuit problem or a part failure

Fuel pressure while cranking has not been checked. I have checked ignition and it is good. I will see if my pump is weak. I am guessing that is where you are headed. Thanks I will let you know