99 Trooper Stalling problem

Stalling problem.
My Trooper now makes me outrageous. It developed the following problems: (1) the engine stalls when I shift it from P to R or when my
foot is off gas pedal. (2) when the engine speed reach 3000 rpm, CEL shows up, (3) after that, the engine idle speed stays at 2000 rpm level and the stall problem disappears. (4) when I disconnect battery cable and reinstall it, CEL become off and the idle speed comes back to normal. But the problem (1) happens again and new cycle begins.
I sent the car to the Bill Stillwell Isuzu in Downers Grove, IL and they told me I need a new fuel pump. Before I send the car back there again, they went out of business. So I have drive 20 miles to a Isuzu dealer at Orland Park, IL. This time, they gave me a even longer list: (1) Fuel pressure regulator (2) Distributor (3) EGR service (4) tune up (5) throttle service (6) Injector service The total quote is $1290 plus tax. Ironically, I just had the 90K service and got new spark plugs and fuel injector serviced 3 months ago. I think maybe I should seek second (or third) opinion.
My fellow Trooper fans, do you guys have any idea what is the real cause of the problem?
is a 99 year model S. It keeps bugging me for a while. The problem began last spring, it was the CEL. At that time nothing else was wrong. I visited my local ISUZU deal for 3 or 4 times. First they changed Intake Manifest gasket. But the CEL came out the next day, later they asked me to dry better gas, so I tried any brand I can find in Chicago, later drive to Indiana to buy gas. But the problem was still there. The last time I visited them, they asked me to change fuel filter and fuel pump. I changed fuel filter. When I made my decision to change the fuel pump (they asked for $900), they went out of business. So I have to find another dealer 20 miles away. This time the sticker shock is even bigger.
So far, the intake manifest gasket was changed twice (at 20K and 80K). I also had 90K service at my local mechanic. they also changed spark plugs (they claim they are platinum) and serviced fuel injector).
According to Edmunds.com, the trade in value of my car is about $4000. Yeah, I am considering get rid of this car. I don't think it is wise to through in $1000 for the repair that cannot guaranty solving the problem. But my wife had a bumper scratch accident with the Trooper last winter, I believe, the trade-in value I get should be less than that. We just got a Toyota Sienna in December. Now my wife tries to persuade to get a Camry. As you know, Trooper owners are the people who don't want to be mainstream. But after all these troubles with this Trooper, I have to think it twice before I get a new car.
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when the check engine light comes on scan the vehicle and see what codes comes up 99 should be OBD2 see if a TCC codes open or short code comes up.this transmission has a lock up torque converter which may cause the stalling problem.. depends on the codes returned from the ecm ...ASE transmission tech...dont buy a new computer for your car have yours rebuilt ask me snipped-for-privacy@bellsouth.net

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