Hi all,

I have a 2003 LM7 in a 1971 C-10, and recently, it has been running completely awful and I really would like some help diagnosing what the issue could potentially be.

First off, when the engine is cold, the truck will barely run and is very lean (I have a wideband to verify) as well as it has almost no power, it is difficult to go up slight hills at 30 mph. Secondly, when the engine is cold, I have noticed via hp tuners that at idle, the truck is producing about 5-10 kpa less vacuum than when at operating temperature (40-45 kpa instead of 35 when warm)

It used to be that once the truck was warm, it would run great, I could smoke the tires without an issue and it was a blast to drive.

Recently though, it is running even worse when cold, and doesn't run much better when warm. It takes at least 15 seconds to get to 60 and is a dog the whole way there. Gas mileage is dismal as well. And when I say no power, it has almost no power. 3/4 is required to go down the freeway at 65 and the wideband afr is all over the place.

I have replaced the intake manifold gaskets as well as sprayed the intake with ether to try and find a vacuum leak, but so far, it appears that it isn't leaking, although I'm fairly confident it is. Right now, I am running on just speed density because I am trying to get the VE table dialed it, but I can't do so when the motor isn't running right.

I can post a data log and tune if necessary

Any help from you guys would be great on what sort of things to check would be great. This is my daily driver to and from highschool and it would be really nice if I could get it running correctly again. I am at the point where I don't know what else to check, which is why I need your guy's help.

Thanks