Well you know the first thing I would recommend is trying a Mopar
Big Block, 383-440 cubic inches should to the trick, if that don't
help then would recommend a crate Hemi and top if off with an
injected and blown intake !!
Seriously though, you've done all the standards and there isn't really
much help in that department without doing some real engine work,
porting heads, larger valves and such and higher comp pistons.
Other than that turbo charging it or adding nitrous is about the only
other thing you can do to make a significant difference.
There is also performance software you can get for a laptop that
you plug into your onboard computer for changing different
peramitters.
Have fun man.........Light 'em up !!
...............QM'r