Jared Moore

I have a 99 silverado 4.8 with 95k miles. Recently I have been having problems with it. While driving around 40-50 it seems as if its reving up and down. its not missing or anything just reving up and down until i punch the gas or just speed up. Also in the mornings when its cold i start my truck and go to press the gas and it hesitates for a second, almost to the point of dieing but it never dies. Help please! Thanks guys!!!!

Fishinfooleric10@aol.com

Let me ask you this for your question between 40-50 mph, does it only do it at these speeds and its not a considerable rev up just 200 or so rpms and almost seems like it has a rhythm to it? For the question about to die question well I have the 99 5.3 z71 and so does my friend and my other friend has a 05 with the 4.8 and ALL of our trucks do it and I don't know why but I do know we all close or over 200,000 miles and it hasn't caused any problems if that gives you any piece of mind.

Let me know your answer to my question on the 40-50 mph.

Jared Moore

Yea it's not a high rev and it doe seem to have a rhythm to it.

Mudd Mutt

It could be down shifting. That's right at the shift point. At 40mph its at about 1100 rpms in 4th gear. You can be pressing down on the gas pedal and keep it in the gear but if you just push a hair harder it'll downshift cause its at a low rpm. If you hit a bump and your foot taps the gas pedal a little harder it'll downshift but when you let back off it'll quickly shift back into 4th. Next time your driving put it into third and see if it still doesn't.

67Motorcat

Here are my probable causes:

(1)Fuel pump is getting tired....replace.
(2) Fuel filter is getting clogged..replace
(3) Throttle valve is dirty...does gas pedal feel sticky?
(4) Injectors need a cleaning...run Seafoam though a tank of gas.
(5) TPS sensor is going (throttle position sensor)...easy to replace.


Start with filter and seafoam....let us know

jesse06

sounds like the trans is having problems with that torque/speed. First couple things you can try before getting into expensive repairs:
Spray down the inside of the carb with cleaner, add carb/FI cleaner to the gas. There is a little plug on the driver side of the trans mission a "shift sensor" try pulling that plug off and driving it around. Check the color of your A/T fliud, it should be red, if its brown you should bring it into a shop in the near future.

Fishinfooleric10@aol.com

Yeah I was asking if those where your symptoms because mine does it too between 40-55 and its because my transmission is slipping and yours might be too. I know thats exactly what you don't wanna hear, but I believe that's what the slight reving is.

Jesse 06 what will taking the plug off do, I am interested to see if it will tell me anything more

Jared Moore

I put in some F1 cleaner yesterday and checked the trans fluid and it looked good . I sprayed the throttled valve awhile back. If the cleaner doesn't work I'm gonna try changing the fuel filter and unplugging the plug. Also after I drive for awhile and stop to check the atm or something while leaving the truck idling. I'll go to take off and it seems to wanna shift hard at the first gear shift. It doesn't do it all the time though

67Motorcat

Keep us posted with your progress.
Sounds like the stalling issues are going to go away.

With close to 100K miles a Trans fluid service is a good idea and just might cure your odd trans issues along with the slight slipping.At around a $100 bucks it is very worth it.

Jared Moore

The serving between 40-50 has seems to stop so far. But I have noticed my truck power has gotten worse. It seems to wanna shift into the passing gear sooner then normal.