At idle. It gets better if i rev the engine in park. But put it in gear and floor it...it responds but your not spin the wheels..its slow. I have checked fuel filter..it clear and clean.

 

Ok. If your excessive fuel trims are at idle, then your line of troubleshooting is the right one - vacuum leak and NOT fuel delivery issue. Does you Montero have a vacuum brake booster or is it a booster pump like in the later models? Vacuum brake boosters can have internal leaks if diaphragm fails. You can try to pinch the vacuum hose to the booster and see if the fuel trims improve. Other suspects: cracked or badly seated air intake hoses. I know it's one of the obvious things, but it never hurts to check again. I once had a crack in the rubber intake hose between the accordion folds. The hole was not noticeable unless I moved the hose around and then I heard the hissing noise. But it was showing up as vacuum leak at idle.

You could check for vacuum leaks using propane bottle. Hook up the scanner showing live fuel trim data; start engine, make sure it runs in "Closed Loop"; take a portable propane bottle (like the ones used for soldering copper pipes), open the valve to let propane flow (do NOT light it up); then point the nozzle around suspect areas on the engine (with engine running) - all around intake manifold, near throttle body, by the intake manifold hose, vacuum hoses, etc. As you do this - watch your fuel trims. When you come to the spot with the vacuum leak, your fuel trim will reduce right before your eyes. If you remove propane - FT will go back up. This way you can pin point where you have the vacuum leak.
This might sound like a very scary method, but it works and it is actually pretty safe. But just in case, have a helper nearby, work outdoors and have a fire extinguisher on hand.

 

Well, i found a bad hissing at the lower bank 1 intake. Replaced both of the lower and the upper intake gaskets. (Felpro). Fuel trims are better, hissing gone. Shrtft bank1 averaging +11 to +16 at idle (750 rpm), bank 2 between -3 and +4. Ot has a small exhaust leak from a terrible welding job at bank 1 just past the pre cat o2 wensor, that may be contributing to my fuel trom readings. My concern is still has no ***** at all at take off. Almost as if its starting in 2nd gear, only not. It shifts perfect and smooth through all the gears and will reach highway speed ......eventually. I really dont feel like it has an engine problem. But i sure would like to call this beast done.

 

Have you ever checked exhaust back pressure? Perhaps you have clogged exhaust?