2001 2500 HD running rough

[Bunky]

I'm getting frustrated, I have a 2001 2500 HD,  6.0 liter,  I parked it for about a year or so and when I got it out it was running rough,   keeps giving me the Po300 code  multiple misfire,    I changed the spark plugs and this did not help,  so I starting looking other places, I found a couple of injectors that weren't working, so I changed them out with some rebuilt ones I bought on Ebay,    I installed them  and it seems to be hitting on the cylinders that were not working but still runs rough but now it pops out the exhaust and I still get the code,   so I changed the  spark plug wires since they were originals, still no better.       I have sprayed the intake and all around it with carburetor cleaner and no change is noticed there,     

 

Anyone have any suggestions ? 

[Colossus]

Injectors- (get NEW not rebuilt, that's just asking for trouble with rebuilt)

New plugs, AC Delco brand ONLY. 

new fuel filter

is all of the old gas out of it? 

How's the air filter? 

Where did it sit during the year?  Any chance rodents got to the wiring? 

Coil(s) may be bad as well. 

What shape is the battery in?

How much have you driven it since you got it out? 

[dewfpo]

DId you fill with fresh gasoline?  Add a full bottle of Techron to clean the fuel system out.Run the heck out of it for a couple of days.

 

DEWFPO

[Colossus]

I'd add 2 bottles, and some BG44K. 

[Bunky]

14 hours ago, Colossus said:

Injectors- (get NEW not rebuilt, that's just asking for trouble with rebuilt)

New plugs, AC Delco brand ONLY. 

new fuel filter

is all of the old gas out of it? 

How's the air filter? 

Where did it sit during the year?  Any chance rodents got to the wiring? 

Coil(s) may be bad as well. 

What shape is the battery in?

How much have you driven it since you got it out? 

Injectors were rebuilt 

New plugs I only use Ac Delco in GM

Fuel filter is fairly new changed just before I parked it

Fresh Fuel and Sea Foam in tank 

K&N Filter cleaned and re installed 

Truck sat Outdoors  I have looked but haven't seen any evidence of Rodents or wires under the hood or Cab  chewed 

Is there a certain place I should look ?

coils ?  I unplugged each one and they seem to be working but might be intermittent

Brand new Battery 

I haven't driven the truck because of how it runs so I haven't plated it.