Cadillac Repair: problems, dodge ram 4x4, viscosity oil

Question

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-----Question-----
i have a 2005 dodge ram 4x4 hemi v8, my problem is when starting the truck there is an extended crank time.  this only happens sometimes though other times it will start with no problem and other times it will start then backfire.  recently when the truck is stopped and in gear the truck idle goes from 750 rpms to 500 then sometimes it drops below and then back up to 750.  the truck has 9,100 miles on it and i just bought it.  ihave drove it maybe 30 days and the dealer has had it for over 2 weeks, they have changed the spark plugs and wires, new pcm, and did something to the throttle body i think the flap in the throttle body was stuck closed.  this is a problem that only does it sometimes, there is no codes and no check engine light on.  today when i was driving it to the dealer to get it fixed when i had it set on cruise the motor would jump back or hesitate.  i need help
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Well im cadillac repair, but your lucky i have chrysler blood in my family...First, it sounds to me that there is a problem with the alternator or the belt, its very easy to replace the serpentine belt. Second, what viscosity oil are you running? Third, run some lucas injector cleaner. 4th, consider replacing the o2 sensor, but with 9,100 miles this hopefully isnt malfunctioning and should be under a factory warranty. 5th, while the engine is running, do you hear any high pitch noises such as a vacuum in the engine bay?



no i don't hear any kind of noise, and the frustrating this is that the dealer is telling me that they may have to just trade me out of the truck because they can't figure out what is wrong with the truck.  this is one of those things that only happens sometimes.

Answer
Because i cant see the truck in person its hard to diagnose this, you could have a faulty ECM, ECU, PCM, BCM and any other computer that connects in any way to the motor, the wiring harnesses could have a short in a wire also. The best way to find out what it is, is to run a diagnostic reader on the obd2 system.