My 1998 Isuzu Hombre will not stay in overdrive I have changed fluid @ & filter also seams like vacuum pressure is high like my breaks r engaged

Breaks = brakes?
the brakes use vacuum but never changes it.
so...... if it does, the booster diaphram is cracked.
OD, can be just a bad OD. switch or more complex.
did you scan the TCM yet if it has one?

why state vacuum high, then not state the values seen?
you connect the gauge, and it reads what? 19inches HG at hot idle is common.
or 0.64 bar (outside usa you use BAR) as you said pressure word for vacuum and is ok in pure science that word) but make me think yoiu are not in USA? or Canada maybe....????

i bet vacuum is just ok.
the issues are with the transmission and its controls.
post is older, are you still having issues.
do say and we can link you up to FSM information on 0D.
the book covers this.... ever see a real FSM before.
the real factory service manual,, (buy one, and win?)
or if in USA , alldata.com is #1 online version of same.....
there are others, but nobody ever posts the country
making most answers wrong, including MINE.

i only have questions, after all im blind cant see car nor open hood.
so... what engine is there, transmissions match engines. so....

omg its really a chebby. Chevy
The pickup was also sold by Isuzu as the Hombre from 1996 through 2000, but only in North America
its not ISUZU at all.
you should know this and post to chevy, S10
2.2 liter or 4.3L engine
my guess is 4.3L with Brazil front sheet metal.

there are 12 control lines from the PCM puter,
and the transmission,
to find out why the OD fails
we first check all fuse..... (on all electric fails we do that)
then check levels hot, by the BOOK.
then scan the PCM for transmission errors, P07xx ? codes>

i look at the alldata. com at the Hombre 98 , pcm page.
schematics.
od .
we make sure no errors from PCM
then check the switch, to PCM for OD active.
if the input is ok.
then we check the solenoid voltages in OD.
if correct then the problem is ok, outside trans, and not inside.

This trans is electronically shifted.
and uses a computer (TCM)
so inputs must be right to TCM
an outputs correct. if not , never blame the tranny first.