Loss of Power

I have a '99 Sierra 4wd extended cab with 80,000 miles. It has the 5.3 motor and an automatic. For the last few months, it shudders when I press the accelerator. As it speeds up, or going up a hill, it makes a lugging noise. I changed the fuel filter last week and nothing improved.

tatobug,

Is your check engine or service engine soon light on? It could be many things, go to autozone or somewere else that can read the trouble codes for free.

My check engine light has not lit up. I went to autozone and had them check the codes, no problems showed up. The guy at autozone thought that I may have a vacuum leak. He noticed that there was a loss of power accompanied by pinging.

Check for leaks around your throttle body,intake manifod or on the vacuum hose. Also look at the thread jerking at highway speeds. Are you using 87 octane gas as well?

My truck was doing the same thing and it ended up being the fuel pump, then later the MAP sensor. The pumps are famous for going out at around 100 k. To test that you will have to check the fuel pressure.

Did you check your plugs and wires too? You could have one thats bad.

The MAP sensor and MAF sensor can cause your problems too. They help the PCM determine the correct air to fuel ratio's.

There are many things that can be causing what your telling me. Do you have a mechanic's repair manual for your truck? It has a section for troubleshooting. Go through the list first.

Curious as to what was the problem with your truck as I have a similar problem with mine. Changed the O2 sensor, fuel filter, plugs etc. and no change. I did notice that if I turned the engine off and restarted the truck would run great for about 45 seconds.

Thank you

Try a can of seafoam on the fuel tank. That stuff they call gas nowdays is a joke.