My 2004 GMC Sierra 5.3 is running terrible. It idles smooth but at highway speeds it shudders and just feels like the fuel injectors are dirty. I took it to the dealer and had the induction system service done but it did no good at all. I haven't hooked up a scanner yet but the check engine light isn't on. Any ideas?
By the way this truck was stored for 6 months prior to me buying it. But I removed the old fuel and have run several tanks through it .

 

Well you're still under warranty, I would insist the dealer takes care of the problem.

 

No it is out of warranty. Purchased from insurance auction.

 

Are you positve that the problem is not in the tranny? Sounds like it could be in trans. Try driving it in the 3 gear position, not D. That will keep it from going into O.D. See if it still does the shuddering.
Keep us posted.

Jim

 

I don't think it in the tranny but I will try that this evening on the way home to rule it out.

 

If you think you are 100% about ruling out the trans, then try this, run majority of the fuel you have in the tank out. Go buy a bottle or two of Lucas gas treatment. Go to a shell or Chevron station and put the bottle or bottles of Lucas into the tank ,then fill it up with 93oct fuel.
About 3/4 of the way through the tank, you should see results if the problem is in the fuel system.
Lucas is one of the best gas treatments you can buy. It has proven itself for many people.
I still find it odd that the truck idles smooth and only acts up on the highway for it to be engine related.
How does it react to WOT blasts from a dead stop to 80 mph?

Jim

 

It isn't the tranny. I ran it in (3) on the way home and it did the same thing intil I got up to about 3000 RPMs. Then it was much better but still had a little skip in it.
Wide open it runs great! But doesn't seem to have the same power my 2001 Silverado had.
I am going to pull the injectors out this evening and take a look at them. I have a set from an engine I purchased to go in my 66 Nova that I would try in it but it is a 2001. I don't know if they will work in this or not.

 

possibly a clogged cat?

 

But he is not having power issues. The reason his 01' felt stronger is because of the amount of TM GM is using in their programs on the newer trucks.
A clogged cat will also sometimes make the engine clatter loud at high rpms.
I think it is something else.
How many miles are on it?

Jim

 

Could it be a faulty ign. coil? It can have good spark at idle,then lose spark at higher rpm's