Ok so it's been a while since I've been on here, I sold my 2006 ccsb I was building for a 2004 avalanche. This is gonna be a little long but I've been having trouble a couple of months now. When I bought it, it was obviously slower than my 2006 given it had a cam, 4.11, programmer and such. But it was still peppy for a 6,600 pound truck. Here in the last couple months it has become severely sluggish at times. On a cold morning start it seems perfectly fine. But once the engine reaches running tempature a it falls on it's face. It also is sluggish when outside tempatures reach 80 or above and humidity is high. By sluggish I mean it has to hit 3-4k rpms to keep up with traffic leaving a light. Any slight hill or speed increase requires a down shift. It feels like your pulling a steel car hauler. Now here's what I have checked. Plugs look good, 20k miles or so on them, replaced wires, used another MAF today with same symptoms, gutted catalytic converters, smoke tested for vacuum leaks, check fuel pressure at rail for 3 days with gauge hooked up and on window while driving with no pressure drops at all, checked injector resistance, and no codes are being thrown. I realize it is a high mileage (200,000mi) 5.3 pushing a beast but it is intermittent. Secondly, last year is started slipping into 3rd gear so I dropped the trans pan and filter. Everything including filter looked brand new and had receipts for trans flush and filter at 120k miles. Well between 6 months ago and now the fluid is completely burnt but the filter is still good with no major shaving. I did haul a small car about an hour drive down a pretty hilly parkway in that time, but it was having these symptoms prior to the haul. I'm not sure what else to inspect. I have access to a computer to hook it up to, to check readings on everything but i don't know what to look for to be causing this. There is no apparent miss or jerking or surging. Just seems to be bogging out and struggling. I ran a fuel system cleaner on a full tank and it seemed to run better, did it again my next fill up with no results. I feel it was just coincidence. I've searched and searched the forum and internet with no similar issues. Also checked tps ohm reading, came back good. Lastly I'll add last year before these symptoms it had a bad pcv valve dumping oil in the intake. I fixed it and cleaned the throttle body. Sorry the post was so long, wanted to include any and all information possible. Oh! I also had a superchips cortex programmer for a while. Seemed to start during that time but I put everything back to stock a few months back. Ran it for about 4 months. So any help would be highly appreciated! I'm at a total loss here and running out of funds doing trial and error fixes. Thanks in advance guys!

 

It's a 2004 avalanche 1500 4wd with the 5.3. Only modification is true dual 2.5" with magnaflows. Had true dual straight pips until I gutted the cats. 197,000 miles. Has a level lift and 33"x12"x18" cooper m/t tires. No other mechanical modifications.

 

My Tahoe is doing almost the exact same things you described. Mines got 240k miles so I just blew it off as high miles and losing power/compression. But if you had a bunch of oil built up like that I'd be tempted to try some seafoam engine treatment. Never tried it personally but have read good reviews about it in cases like this.

Mike

 

I sea foamed it by a can in the gas tank, and half a can through the vacuum line. No results either way

 

Holy run on sentence batman..

If your fluid is burnt after 6 months, There is no way that trans filter is any good.

I only use OEM type replacement trans filters that I buy from a local trans supply warehouse. The ones I have found at the parts store are usually either the wrong length, have a cheaper media, or don't fit correctly and can cause pressure loss issues.

A clogged trans filter can give a sluggish feeling. Just because there is no metal in the pan or filter doesn't mean the filter is still good. Clutch material can restrict the filter. especially if the fluid appears or smells burnt.

If your fluid is burnt and you have slipping in 3rd you trans is on its way out.


BTW not sure on your service history 6 months ago but GM recommends you replace the filter every 50,000 miles.

 

Sorry this was posted late last night off a cell phone. I was more worried about just making sense. Lol

But, I do understand it could make it sluggish. But just this morning it ran like a scalded dog and never made it over 2k rpms with plenty of power up the big hills in my neighborhood.

To put it in perspective this morning in my driveway, which is pretty steep, I put it in reverse and it almost backs up it while idling. If it's hot outside and warmed up, you almost have to floor Matt it just to get out of the driveway. It won't even spin a tire in gravel or the yard after a rain when it's being sluggish. But when it's running good I've cut donuts in a wet parking with ease.

 

So when its cooler outside but the truck is at operating temps it still runs good? Almost sounds like a faulty IAT sensor maybe?

Mike

 

I am having similar issues in a 2001 gmc 5.3. Found a LOT of water in the tank and filter, replaced pump and filter(pump failed anyway) and happened on 2nd tank of fuel after rainy weather.

 

It's hot and it don't like it.