Good to see you’re writing again.
Don’t worry about getting the science right in the first or even the second draft. Just make it plausible.

Just get the drafts done.

Then go back and edit.

Obsessing over the details of the science and tech is just another form of procrastintion.

I’ve read a lot of sci fi, and I read it more for the interesting plot- the story/scenario -rather than the accuracy of the tech.

One or two cool tech concepts- three at most- put the sci in sci fi.

Just get it done.

So what if GPS jumped the reality gap and now can exist in PDAs or helmets.

Embed the circuitry directly in the main characters brain (like George Alec Effinger did with skillware and VR in When Gravity Fails http://en.wikipedia.org/wiki/When_Gravity_Fails )

Since it sounds like you’re going for some kind of ‘Ghost’ mythos along with science, make it cutting edge beta ‘ware with bugs that include ghost like hallucinations drawn from the main charcters subconscious memories (a great way to do flashbacks or training recaps too).
As a subplot, your MC could be desperately seeking a service pack/patch to update his experimental buggy beta ware.
And who has it?
Only the villian, of course.

Don’t Think about it.
Do it.
Write on.