2004 Yukon XL occasional slow 1-2 shifting

['63GENIII]

Hey guys, I'm usually on the 60-66 side but I'm servicing our '04 Yukon XL (Denali with the 6.0) for a last minute trip to San Diego for my daughters softball next week. The question is with the transmission which has had an occasional 1-2 slip when warmed up. It has done it for the last 40K and we have just lived with it, meaning when it does it once, we baby it through a few cycles of the gear shifts and it seems to go away. So far so good right? Well I was thinking about changing the transmission fluid this weekend and am wondering if there is something that I may possibly be able to repair while I'm in there or am I possibly about to open a can of worms by doing this service a week before a long trip like this in the first place? I really don't want to take it to a transmission shop because I know they will tell me that I DO need a new transmission ( I actually took it to one when we first got the car and that's what they said). I kinda trust the opinions of the members of the forum a little more than alot of the shops that I've found. Anyway, is there something that I should be looking at - for when dropping the pan, or is it a bad idea to even open it in the first place before a long trip when I don't have the money to replace the trans in the first place? I appologize for the novel, just trying to get an opinion from a well respected source.

['63GENIII]

So I took it out today to run some errands and try as I may I could not get it to do the 1-2 shift slip that happens once in a while. I was gettin on it pretty good and it was shifting pretty good. Almost like it knew it needed to firm up the shifts cuz I had my foot in it. Most of the time when it doees do it though, it's during normal driving and when you'd least expect it. When it does happen on light acceleration, I just lift a little and it goes right into 2nd. Any thoughts on "power flushing" the transmission? Could there be some debris lodged in a valve or possibly affecting some of the electronics that flushing would dislodge?

[clinebarger]

Leave it alone, Get there & back.

How many miles are on your truck?

Im guessing you have a 1500 with a 4L60E? A 2500 would have a 4L80E.

['63GENIII]

Sorry for not mentioning that it's a 1500. Yes 4l60e. Ive been trying to research a little on my own and keep reading about the stock programming being "adaptive". Could this be part of the problem? Im taking your advise Cline and Im not doing anything before the trip except checking the fluid level. I would really like to figure this out though now that it's on the radar. Is there a good place to start?
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Posted via Mobile Device

[clinebarger]

Originally Posted by '63GENIII

Sorry for not mentioning that it's a 1500. Yes 4l60e. Ive been trying to research a little on my own and keep reading about the stock programming being "adaptive". Could this be part of the problem? Im taking your advise Cline and Im not doing anything before the trip except checking the fluid level. I would really like to figure this out though now that it's on the radar. Is there a good place to start?
Posted via Mobile Device
Posted via Mobile Device

The PCM has "Adaptive Shift Strategy", Most likely not the problem.

The most likely cause is a worn 2-4 band or too much 2-4 band clearance.
The good thing is the 2-4 band is the "toughest" friction in this transmission, Even a worn band can be "shimmed" & work OK for awhile.

A TransGo SK 4L60E shift kit http://transgoonline.com/products.ph...dcountview=Yes works REALLY good, Can be installed while it's in the truck.

['63GENIII]

Thanks CB I will check it our when we get back. Any idea why the slippage or soft shift is so infrequent? Seems like it's going to be tough to troubleshoot until it starts happening more often.