I was driving on the interstate, empty, Edge on 2 and no propane. Had it on cruise control at about 75 going up a gradual hill.

It down-shifted into 4th and I thought...wow, it never downshifts on a hill like that. It also started losing speed quickly and it had no power...could barely hold it at 60 and still wouldn't shift into 5th.

I pulled over and it seemed to idle and run fine while parked...no SES light. I shut it off and started it back up and it still seemed fine. So I took off again and still no power. Everything seemed normal but no power so I called OnStar and had them scan it. While they were scanning it the SES light came on and all of a sudden it came back to life. Went from about 55 to 80 like a rocket...like it usually does. I also noticed the boost gauge jumped up...for some reason I didn't look at it while it had no power.

OnStar came back and said it set 2 codes...both had to do with the intake/boost condition. She couldn't give me the code numbers because she said that dept. wasn't working today.

It ran fine for the 175 miles left to get me home and it seems to be fine now but the light is still on.

I think it went into a zero boost condition for some reason. Anyone have any ideas?????

Sounds like a 1093 or a 238/299. Probably a 299 from the boost stick. All three of those codes cause limp mode. Your truck was in an engine limp or trans limp mode.

It could be a 0700 trans limp. We won't know until you get the code numbers for sure. Buy a Predator so you can read codes. I'm betting on the 299 from the info you gave so far.

Ill Bet On Egr Valve.

Well OnStar couldn't give me the actual code numbers and they cleared themselves before I could get it scanned.

I think it was a 299/238 like bobo said.

Would it be an EGR problem if I have it blocked?

Also, would the 299/238 clear/fix itself while I was driving? It came back to life while I was driving down the highway.

What would cause these codes just droning down the highway?

Could it have been an intermittent in the boost stick?

I've had the boost stick on for about 6000 miles now without a problem.

238/299 is common with an aftermarket air filter and a boost stick. Putting on your stock air box could clear the problem.

Well OnStar couldn't give me the actual code numbers and they cleared themselves before I could get it scanned.

I think it was a 299/238 like bobo said.

Would it be an EGR problem if I have it blocked?

Also, would the 299/238 clear/fix itself while I was driving? It came back to life while I was driving down the highway.

What would cause these codes just droning down the highway?

Could it have been an intermittent in the boost stick?

I've had the boost stick on for about 6000 miles now without a problem.

The codes should be there if you get to a Tech 2.