2001 Isuzu Rodeo Sport will not go forward in drive

automatic trans or stick, we cant guess that ever.....
REVERSE OK!
drive, and Low dead. (hot and cold engine????)
so does it slip.?
slip means, you step on the gas and RPM races but car dont move. SLIPs. that is transmission
but of it dont slip that means the engine is weak..
if its slip?, check levels first.
if levels in box are ok (dont guess read how to )
then check shift linkage.
if that is ok, scan the PCM for tranny errors DTC.
if that is ok, do the FSM stated, line pressure tests..

Did you by chance have it Back flushed in a service center if there is lots of mileage on this 150K plus more than likely the transmission is done for NEVER back flush a transmission i dont care what people say.

Isuzu Rodeo offers a lightweight V6 engine, push-button four-wheel drive, sturdy construction and lots of cargo space.--------------------------------------------------------------------------------
MaxiScan FR704 Code Scanner Reader

Check for leaking intake gasket.

I tried the DIY service and repair manuals from a website and it actually helped me repair transmission problem in my jcb 3cx site-master. it wont move forward or reverse, engine is good both solenoids for
forward and reverse work.
I don't have much technical knowledge but I just followed it step-wise, and works perfect! got it from www.reliable-store.com

Transmission is shot.

check fuses and relays.

reduced power usally points toward a gas pedal to throttle correlation meaning the drive by wire system is where the problem is

It may be a Throttle Positioning Sensor, or TPS for short. Is the engine light on, and if so you can get it scanned at any local advance auto or autozone for free to tell you what it is. If it's not the TPS, checking simple preventitive maintnence areas, like tune up, if it hasn't been done in a while, it's a good thing to do.
Hope this helps