Sierra transmission shifting help

[Boosted131]

On my 99 Sierra with the 5.3L I am having a bit of a problem. While towing yesterday with cruise on it will downshift on the hills then when it levels out, it won't upshift again until I turn off cruise and let off the throttle a tad.
Seems like it's also shifting later than it should but not sure on that one.

Also is there a good forum for these trucks specifically?

[master hec0]

Hows the condition of the trans fluid? Does it read low? When was the transmission last serviced?

I would suggest you flush your fluid and replace the filter and see if your issues continue.

[FraserB]

^ Do that.

GMFullSize or SilveradoSierra are both decent forums

[HiTempguy1]

Originally posted by Boosted131
On my 99 Sierra with the 5.3L I am having a bit of a problem. While towing yesterday with cruise on it will downshift on the hills then when it levels out, it won't upshift again until I turn off cruise and let off the throttle a tad.
Seems like it's also shifting later than it should but not sure on that one.

Also is there a good forum for these trucks specifically?

Well the first question is, are you actually on flat ground/not facing a headwind that allows the truck to pull the load you have on it in 4th OD with the torque converter locked? There may be variables at play that you haven't considered is all I am saying.

As for the "shifting later than it should", keep in mind that after 160,000kms, the 4L60E is practically a ticking time bomb (it's extremely well documented, I'm not over-exaggerating). There are multiple failure points that weren't addressed until the 4L65E/4L70E came along. You might be getting due for a rebuild

[Boosted131]

I'll have to check the fluid then, my dad has owned this truck since new and it only has 250,000 km and has never had any real problems...

It's not the wind because I can turn off cruise control and pull it in overdrive no problem. This is a fairly light load too, just 2 quads and a trailer

[71/454]

I would caution against flushing the fluid.

Check the colour first, if it's redish brown it "should" be ok to change.

If it is black, dark brown or has crap floating around in it I would not change it as this is the clutch material and may be the only grip your clutches have left. Changing the fluid may serve to make the transmission not work in any gear.

At 250xxx kms if it has not had a rebuild it likely doesn't have a ton of life left, I would go easy on the towing.

[ddduke]

Originally posted by HiTempguy1

As for the "shifting later than it should", keep in mind that after 160,000kms, the 4L60E is practically a ticking time bomb (it's extremely well documented, I'm not over-exaggerating). There are multiple failure points that weren't addressed until the 4L65E/4L70E came along. You might be getting due for a rebuild

This.

The 4l60e is shit, we've had more of them go on company trucks then I can count.

[AE92_TreunoSC]

Plan on a rebuild soon, especially because you tow. The 4L60 is lucky to get to 100 under severe conditions.

Take it to a reputable transmission shop and have them drive it, usually they get in and watch the data stream on a quick drive, within a minute they can tell whats wrong.

Internet can rarely diagnose transmission issues, aside from fluid level there's not much else to assist with.

[Boosted131]

I noticed after today that it shifts later than it should now too, like hardly pressing the gas it will rev like 3000 rpm then shift. Weird because I towed the day before and it was perfect, now this.

It has towed most of it's life though, 5th wheels, boats, etc.
How much is a rebuild on one of these? I'd love to keep the truck since everything else is great

[71/454]

I think a good rebuild would be around $1800. The good news is they can be built to be tougher than stock and will handle some towing.

[Boosted131]

Well my dad took it and said it was running perfect last night, then I drove it this morning and it was fine as well... Not sure what was causing it to shift slow earlier

[HiTempguy1]

Originally posted by Boosted131
I noticed after today that it shifts later than it should now too, like hardly pressing the gas it will rev like 3000 rpm then shift. Weird because I towed the day before and it was perfect, now this.

It has towed most of it's life though, 5th wheels, boats, etc.
How much is a rebuild on one of these? I'd love to keep the truck since everything else is great

Depending on how much your time is worth, I know a gentleman in Spruce Grove (near Edmonton) who is a licenced gm tech that has his own side business strictly.rebuilding and replacing 4L60E's and gm transfer cases. He'll do a complete removal, rebuild, and reinstall for $1500 (and the tranny is modified for towing with better bands, a different shift servo, a torque converter that won't explode, etc). He can do a normal stock rebuild (but still update the most critical parts that are known to fail) for $1250.

Any other transmission shop wanted $3k for all of that. I've down strictly towing through the mountains (close to.30,000kms with it now) and no issues.Any shop that quotes you below $2k is doing the absolute bare bones minimum to get the truck bacl on the road... you can get "rebuilt" trannies on kijiji for $750 to $1k, but they wont survive towing very long.

[Boosted131]

What's the turn around time on that guy?

[Boosted131]

Yay it has a throttle position sensor code, which I think relates to the late shifting?