2004 peterbilt 387 w/c-15 cat motor. at idle motor shakes. going down road motor causes whole truck to shake. coolant temp at idle wont go above 150. temp wont go above 190 even at hard pull. truck loses power frequently, makes a gurgling noise. ehaust now has low moan, turbo boosting ok, flames out of exhaust pipe occasionally, jake brakes sound high at times and little or no sound at others. Any clues here no eng codes coming up and shops just cant figure it out??

Have you checked for vacuum leaks? Poor idling when cold that gets better when the engine warms up, or at higher RPMs are symptoms of vacuum leaks. Check all hoses and connectors. If it's a manifold gasket, you will want to use a smoke machine (check when the engine is cold).

Tune up and the correct timing needs to be set when you are done with new cap and rotor, try that first, when you remove the cap do not turn it just lift it off or the timing gets messed up.

Possible dirty EGR valve, or bad ignition module. Could also be many other things, coolant temp sensor, bad cat converter, clogged muffler, etc.

I really need to know the mileage.....?..also the question isn't very clear ...Is the whole truck shaking roughly or is the engine shaking roughly or is it both the engine and truck shaking..?..Since I am not sure I will answer what I can....Ok......If the truck is shaking while sitting still at idle the engine/trans mounts could be worn and or loose mounting hardware...If the engine is running roughly at idle causing all to shake that bad it could be a number of things causing it as usual...Quite often a faulty plug wire/and or bad plug will make it have a misfire because it will be running on only 5 cylinders..If that's the case it could be more than one bad...A vacuum leak will cause it to perform in the same manner...however all cylinders will be firing..Normally a vacuum leak is easy to pinpoint..however it could be a faulty IAC valve..(IDLE AIR CONTROL)..The idle air control is designed to hold a high idle at start up then slowly bring idle down to proper Rpm.....A faulty TPS (THROTTLE POSITION SENSOR) will also cause a rough running problem..And let's not forget the O2 sensor..(OXYGEN SENSOR)..The O2 sensor controls air/fuel mixture...and yes an exhaust manifold gasket will make it run rough but not too bad...It has a rough running sound more so than causing it to horribly shake..It will shake but not to bad..
it is located at the exhaust side of engine..The exhaust manifold is mounted to the engine exhaust port..the exhaust pipe is mounted to the exhaust manifold and the muffler/cat converter is mounted to the exhaust pipe...You can check the plug wires quickly..With engine running carefully remove plug wires 1 at a time..If the sound of engine gets worse the wire you removed is good..after verifying it is good or bad plug wire back on then pull the next wire..and so on..If you pull a wire off and there is no change in engine operation that is the bad wire..If that is the case change all plugs and wires...One at a time..(It is a good idea to make sure all wires come off easily before starting engine..old wires will come apart easily..grasp wire tightly at boot and twist left to right while pulling..)as far as the other components I spoke as well as many others,the best,easy way is to have it hooked to a scanner and they can check/test all components for proper operation...Now..If it runs good but is shaking the engine/trans mounts are worn as I stated earlier..any loose engine component will cause an engine shake also but you should notice it at a glance...engine mount bolts/nuts being loose can be tightened without changing mounts if caught in time..Trans could be coming loose.also worn clutch will cause vibration...Send more info and I can guide you to remove and replace any faulty components you may find to save you money.........Brooks/Metalpoet.....

Look for a vacuum leak.

I doubt the cat would cause this problem. It sounds like electrical to me. Did the tune-up include everything? I would first suspect a spark plug or wire. Then maybe look for idle adjustment.

Shakes ONLY under acceleration? Goes away when you back off of the throttle? Are you sure?
Please inspect the front and both side engine mounts.The half shafts will cause that sort of a shake(whole car) when they go bad(inboard CV joints).
Aggravated OR caused my a motor mount that has shifted to one side,binding the half shaft.
Common in Chrysler mini vans!!!!!!That is why the front motor mount is adjustable.
Check the engine mount on the short half side first.

You have a random misfire issue follow the link for info on this problem. Problem 6 Engine Stalls Misfire Code Cylinder Misfire

Well this could be caused by a number of things. But the most common cause is an "engine miss." You could have 1 cylinder that has stopped firing. This will cause a very rough idle and very possibly shake or shudder whenever you accelerate. Another cause may be a main "vacuum hose could be disconnected" from it's port. Vacuum leaks cause engine shake at idle. Check for loose, cracked, or disconnected vacuum hoses under the hood. The third and least likely cause is a "broken or worn motor mount". If the engine is not securely held down in place by all the motor mounts, it will vibrate excessively and cause a shake at idle. The engine miss and motor mount problems are 2 issues best left to a professional to tackle. But as I said, you could tackle the vacuum leak issue yourself by checking under the hood. Hope this helps, good luck!

mass air flow sencer and idle sencer