I've been having serious buzzing problems with my EJ strat and I don't know what the problem is. There is a lot of buzzing when playing an open low E. The buzzing occurs at every position across the 3 lower strings and the G string as well. The neck relief seems to be fine. I've also tried to change the saddle heights but that won't work. I've also put the GHS Eric Johnson strings but it didn't do any good. I need help desperately!

The GHS ej sig strings are heavier gauge in the lower strings than the normal 10's, so will change the set up slightly. The neck relief and saddle height specs are a guide only, you need to find a spec that suits you, which may mean a little more relief.

Have you checked the pickup height? The magnetic pull can cause buzzes if too high.

It is probably worth getting the guitar along to a good tech; it just may be that a fret is too high or something, and they can check the set up for you.

Mine is still a bit buzzy after much tweaking. But then so is my masterbuilt strat, which has had a plek set up! I've noticed technique makes a difference too as in fretting the note well.

I know that Eric Johnson is a tone freak. Would the change in the pickup height cause any change to the tone? This is something I am also concerned about.

It does. Closer to the string means more power, but less sweetness I think. Too close and you get weird notes and resonances. Experiment, you won't do any harm.