performance upgrade advice please

I've a F23Z4 motor in a mid 2003 Odyssey (previous shape before the new
lower"sporty" shape) and would like any advice for upgrading its
performance. I'd like to increase its midrange torque mostly as we find it
gear hunting a lot on long hills at around 100klm/hr.It also kicks down too
easily at middrange revs, even if it only has 500rpm remaining to the
redline.
Has anyone good or bad experience with chip upgrades, exhaust systems and
other bolt-on mods etc, or should I be looking for more extensive work such
as a supercharger?

 

its a fuckin van dude. a 4 banger at that in a heavy vehicle. Maybe remove
some of that un-needed weight like the doors or something. and you'd be
surprised what some speed holes can do in the hood.

 

Maybe just downshift on the hills?