Highway On 5.3 Silvy Real High Rpm And No Accel

99silverado1500 · July 1, 2007

On my 5.3 silverado, on the highways, is kinda sluggish. At 65 mph, im running like 2200 RPMs, but with my exhaust makes it sound like its like out of juice. I know I shouldnt be doing this, but I was on a stretch of roadway that was barren this morning, and let er rip, and I was doing approx 95, and it was running in the real low 4000 rpm range I know i was real close to the shutoff point but still should the RPMS be that high?? I think it needs a gearing change. I BELIEVE it has 3.42s. It is what i was told, and the original owner believed that it had the 3.42s. Should it be acting like this, or might I have a 3.73 in my truck? But rolling on the highway it seems to be dead though, and I cant really have fun like I do in the cities, because it doesnt pick up when its rolling that fast. Any advice would be great!!!

brnr17 · July 2, 2007

dont mean to hijack the thread but how can you tell what gears your truck has?

J45p3r · July 2, 2007

Read this chart http://www.fullsizechevy.com/forums/showth...highlight=gears and find the code in your glove box.

svensk · July 2, 2007

Those rpms are way too high for 3.42's. Unless you were running in 3rd gear, 2200 @ 65 would make more sense.

Tucson_02Silverado · July 2, 2007

I have 3.73, at 2000rpm i'm running 67mph.

You either have 4.10's or have lost overdrive in your tranny if you indeed have 3.42's

99silverado1500 · July 2, 2007

I have 3.73, at 2000rpm i'm running 67mph.

You either have 4.10's or have lost overdrive in your tranny if you indeed have 3.42's

I have overdrive...I am thinking I have a 3.73 axle ratio. It has 97000 miles if that means anything. Ill check the glove box now and see what I really have. Also I was cruising with cruise control, and it seemed to be in overdrive, but Ill check the ratio and then Ill see what happens from there.

cmoore74 · July 2, 2007

I don't think the 3.42 gear ratio was even available for a '99 Z71.

2200 RPM at 65 MPH is too high for 3.73's. At those RPM's I would say you have 4.10 gears.

99silverado1500 · July 2, 2007

I went out and checked....3.73 axle ratio....I have codes GT4, and G80 in my glove box, which is 3.73 Limited Slip. Is it possible to change it to the 3.42? Also if I can change it to a 3.42 how will it act? My truck is real good now, picks up and moves, quick, but the highway its real high rpms. How is the 3.42 on the highway and how is acceleration with a 3.42? Thanks for the help so far and eager to await replies.

svensk · July 2, 2007

What are you even asking now that you've confirmed you have 3.73's? Is there something wrong with your truck? Is it too slow or too fast for your liking? Why would you possibly want to change from a 3.73 gear to a taller 3.42? That would make your truck slower from a stop.

99silverado1500 · July 2, 2007

What are you even asking now that you've confirmed you have 3.73's? Is there something wrong with your truck? Is it too slow or too fast for your liking? Why would you possibly want to change from a 3.73 gear to a taller 3.42? That would make your truck slower from a stop.

Well is it going to loose a LOT of acceleration, or will it matter, I just do not really like how it drives on the highway at all. It has no power on the highway really to pass or to accelerate. Also would a 3.42 help with fuel economy at all? I would like to change to the taller 3.42, would like to know what all other then little less accel, what will be changed by moving down to a 3.42

cmoore74 · July 2, 2007

The 3.73 gears are arguably the best gear for these trucks. Some don't like the 3.42's because they are not good for towing heavy loads and some don't like the 4.10's for the high RPM's required to maintain speed when not towing. The 3.73 gear is a good gear as it is right in between.

Switching gears on a 4x4 (i.e. front and rear) will cost upwards of a couple of thousand dollars at the dealership.

2200 RPM still sounds a bit high for 65 MPH with 3.73's. Are the tires the stock size? Smaller than stock size tires would result in a higher RPM (assuming the speedometer was recalibrated for a tire change).

emejay · July 2, 2007

Those rpms are way too high for 3.42's. Unless you were running in 3rd gear, 2200 @ 65 would make more sense.

I agree, those rpm's are way too high.

99silverado1500 · July 2, 2007

I am not sure the tire size off hand, but they are the largest size that can be on a stock silverado if I remember right. The fronts rub a little when turning real hard. I will be on the same road today and I will see what it does again to confirm what I saw, with the RPMs to speed. It has the 3.73 ls...not the 3.42s. If its going to cost that much to do a change, i might just deal with it for now, and get a new truck in the future.

cmoore74 · July 2, 2007

If it's rubbing, or close to it, those are probably larger than stock tires. It could be the speedometer was never recalibrated for the tire change and you're really going faster than you think. This would explain the high RPM for the speed.

You could either have someone pace you or if you happen to have or can borrow a handheld GPS you would be able to tell what speed your really going.

99silverado1500 · July 2, 2007

If it's rubbing, or close to it, those are probably larger than stock tires. It could be the speedometer was never recalibrated for the tire change and you're really going faster than you think. This would explain the high RPM for the speed.

You could either have someone pace you or if you happen to have or can borrow a handheld GPS you would be able to tell what speed your really going.

I have a Garmin C340 installed in my truck and also own a handheld but wasnt using it yesterday or any of the other times really. Im leaving in the next half hour, so ill compare it to both of my GPS's and see what its really doing.