There's nothing you can tune with a stock ECU that can change fuel mixtures. You'll need an engine management system for that. I believe Nistune are a popular choice for the 4.2 EFI.
A good fuel pressure regulator is a must. A 1 to 1 ratio boost reference will increase the fuel pressure by 1 psi for each psi of boost. This will compensate for the injectors trying to open against the increased manifold pressure.
It's common practice to also raise the base fuel pressure but this will cause rich idle if the ECU can't adjust sufficiently.
It can also make the standard fuel pump work harder.
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