My 1999 Isuzu Rodeo Manual Transmission runs great, the vehicle gets 25mpg highway... but I want more MPG and I believe it''s possible. The manual transmission is geared low (about 3000 rpm @ 65 mph). I have long thought if I could replace the 5th gear with a smaller gear for a super-overdrive I could significantly increase the mpg.

1) Any thoughts on how I could proceed on that? I can''t find any service manuals for 99 Rodeo tranmmissions.

2) Is this a silly idea?

many thanks,
a.t.