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4l60e Rebuilt in 2018 Giving Me issues

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So, I have a 2002 GMC Yukon 5.3l 4l60e "Stock" Got about 90,000 since the rebuild give or take I Changed the filter and fluid at around 60k. Of course, I didn't do a complete fluid change just a flush I think it was 4-6 Qts. or so. I put some Lucus Fluid Conditioner in it not really needed but I always put at-least one bottle in. I CHECKED THE FLUID LEVEL AFTER I DID IT 20 TIMES! Remember i said that.... lol

Today I drove about 12 miles to Walmart noticed it was kicking in and out of 4th to 3rd and back to 4th then 3rd every few seconds while I was maintaining a speed about 45 to 55.

Went to Walmart Came out Started driving back home at first it was fine about 3 miles from home same thing. Here is what I know....

When it warms up it happens not when cold. I checked fluid at home. It was actually high. I checked it in park running of course. No lights not even Check engine. Engine has about the same as it was rebuilt same time. Truck just hit 350,000 today! :( everything runs great. but the fluid was actually about an 1inch or 2 over the hot. when I checked it, me and my pops looked together at it, and he agreed it was high. I don't have a tranny scanner, and no Drain plug as the welded it for some reason when they did the trans not sure why, but some people around here say that's normal? idk, but any help would be great.  Pops wants me to Wait to drop pan cause of oil cost and get a scanner on it which I don't know anyone other than trans shop that has one. Money is kind of tight right now, but I want to know what the pan or filter has to say. It's eating me alive tbh.

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First question that comes to mind is, was the correct fluid used?


Just FYI to avoid confusion, a flush is a TOTAL fluid change. You flush either with a machine, or by removing a cooler line and pouring fluid in constantly until it comes out the disconnected cooler line as clean as it's going in. Then you drop the pan and change the filter, add quarts and flush another 4 or more (Or whatever way is your preferred way). This puts fresh ATF in every part of the transmission, including the torque converter. Sounds like you just did a "spill and fill" - drop the pan, change filter, add 4 qts..


Are you sure it's actually going from 3rd to 4th, and not going from 4th to 4th lockup and back again?


After doing a spill and fill, you need to add the 4 quarts or so to get the level normal, THEN run through ALL gears to the bottom, then back up top to park, pausing for 3 or more seconds in each gear, including neutral and park. This is super critical on a newly rebuilt or replaced transmission, with the addition of hitting lockup on a test run. Reverse alone is a HUGE circuit. For just a fluid spill and fill it's unlikely the lockup (Or any other) circuit will go dry, but never hurts to do the procedure anyway. If any of those circuits drained down, you'll notice a fluid drop after going through all the gears, and then again after a lockup event.


Another thing to note is that you never fill the transmission to the full mark ... UNLESS the transmission is at FULL operating temperature. Somewhere north of 140°F.

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Ok, so yes of course correct fluid was used Dex VI as that is the recommended fluid. also, your right I just did the filter and fluid change not a flush my mistake. thanks for clearing that up. and yes, I did all the above you stated. also, I want to point out 15k ago I did the trans fluid and filter. it wasn't rebuilt then... it was rebuilt about 80k ago... and when it hit 60k as recommended by the manufacture I did the fluid change and filter. or as you say spill and fill.

And yes I am sure its going from 3rd to 4th. 50MPH 2000 rpm's... about... might be little off.. at 50MPH when it does go into 4th aka OD... it sits at 1300 to 1500 RPM.... its going down to 1400 to 2000 back to 1400 back to 2000... these types of things especially while having an exhaust are very noticeable. you cant mistake that for anything else.. also when going up to 55 to 65 MPH it doesn't want to shift into OD unless I let off throttle. it goes all the way up to like 2500 to 3000 rpm or so... so yes I'm sure its got the issue I described... and once again yes I filled and did the procedure correctly over 15k ago.. if I didn't I would've seen something go wrong way before 15k... of course the trans was hot when I topped it off after changing the filter. I defiantly checked it and for the next 3 days after rechecked after driving. I ALWAYS OVER DO IT WHEN IT comes to my vehicles. I always over check everything I am the guy that changes his oil even though I know its a little less then 6 Qts but checks the dip stick like 5 times. wipes it off each time.... I never noticed the the fluid two inces over the hot. but either way Were here now, so what could it be?

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Good to know. Don't take it personally. I have to ask dumb questions, because some who post here lack even basic mechanical knowledge of ANY system - sounds like you know what you're doing.


2" over is pretty overfull. I'm wondering if the trans is severely overheating for some reason. If it is, the fluid level would return to where you set it prior after it cooled off overnight.  If there was coolant getting in there, you'd immediately notice the strawberry milk shake on the dipstick. You could have a seal leak - is this 4x4?  Maybe transfer case fluid is getting into the trans.. Usually this is the other way around, though. The case vent would have to be plugged solid and the case becoming pressurized. Long shot there. Could be a failed lockup circuit or solenoid, or torque converter itself.


I'd also want to see what the MAF is doing. MAF problems have burnt up MANY transmissions. You'd more than likely have a MAF code if this were the case, so if the money light isn't on, I'd just check the grams per second at idle with a scan tool - if its 5.3 or reasonably close, it's ok. If not, give it a careful cleaning.


Could very well be an internal transmission issue. Without actually driving it and seeing / feeling what exactly is happening while watching scan tool data, it's impossible to say from here.

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When you filled it, did you follow the procedure outlined in the owners manual for checking the fluid level?  It's more than a 1 minute task...


Don't know why they would weld your drain plug in place, when I rebuilt my 4l80e, I added a drain plug to the pan.  It makes the drain a bit easier/less messy compared to lowering the pan and having it pour from a corner.


And your description of your fluid change doesn't really make sense.  The "normal" thing to do is a pan drop/filter replace, and that replaces only about 1/3 or so of the fluid.  A flush replaces all the fluid.  Maybe describe what you actually did to change the fluid?

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Oh yeah, all kinds of stuff can be wrong and the CEL will be off, it's only used to notify you of emissions related problems, not problems in general.


I would suggest getting a tech ii from ebay/amazon, not that much more than a more advanced code reader (one that can get stuff from the tcm, abs, srs systems), but it can read codes from all the computers in your truck (there's more than 10, varies with what options you have).


You can pay to diagnose the problem, or pay to randomly throw parts at it hoping to fix it...

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