Before telling me 3-4 clutch packs please here me out & please be patient with me.. so I have a 02 gmc sierra 4.8 with 4l60e. A year or two ago I changed out my 4l60e with a used one only because my original one was kinda slipping but only when going over a mountain I commuted on beside that no other issues so I changed it out before it went out with a used one & kept the original one in my yard just in case... so the last year or so the used transmission I put in has been working perfectly never had any issues shifting or slipping At All!... a few weeks ago I drove to work parked it when I got back in it to drive home, put it in Drive, 1st was fine 1st-2nd was fine as soon as it shifted 2nd-3rd, in went into 3rd for a moment then revved right up like it was in neutral, wouldn't go into 4th at all even if I was able to get my speed/speedometer up to the mph 3rd or 4th should engage, though it was low on fluid, put some in, same issue proceeded, so I had to drive home in 2nd gear... so like any one else would think, my 3rd-4th clutch packs are gone, needs rebuild or new trans.. Soo I dropped the trans, grabbed my original trans I had sitting in my yard, stuck it back in, went a test drive & had the exact same symptoms happen, 1st-2nd just fine no hard shifts or slips but 2nd-3rd, shifts into 3rd for a sec then revves right up like it's in neutral & no 4th gear at all, I do notice if I have it in 3rd & let it almost redline it engages but I think it's only just down shifting into 2nd.... SOO LIKE WHAT AM I MISSING OR DOING WRONG FOR 2 DIFFERENT TRANS DO THE EXACT SAME ISSUE??? IS IT REALLY POSSIBLE TO HAVE 3RD-4TH CLUTCH PACKS JUST RANDOMLY GO OUT ON 2 DIFFERENT TRANS LIKE THAT OR HAVE THE EXACT PROBLEM BACK TO BACK LIKE THAT & IM JUST NOT ACCEPTING ITS THE CLUTCH PACKS? IF SO THEN WHAT IF I CHANGED THE TRANS WITH A NEW ONE OR REBUILT ONE & GO TO DRIVE IT & HAVE THE EXACT SAME PROBLEM OCCUR??? WHAT WOULD MY PROBLEM BE OR POSSIBLY BE AT THAT POINT?????? I'm not at mechanic I'm not a 4l60e expert. I'm just a 35yr old 4th gen plumber who is mechanically inclined to understand mechanical problems & solve them myself cause I'm too cheap & got to much pride to pay someone else to fix/do the work I'm totally capable of doing, never once ever hired a mechanic in my life & I'm not about to let some 4l60e make me have to!!! I don't care, call me stupid or any names, you can't shake my tree because of the ******* old man who trained me the right way... so shout out to all you ******** who still practice these techniques🙏

Please read the entire thread before saying 3rd-4th clutch packs please...

 

1st off didn't you remove the 1st transmission because if was slipping? Why would you think it would work after sitting in your yard for 2 years?

For the trans to be holding 2nd gear and then shift and then slip, that sounds to me as if the electronics and valve body are working as they should. You could hook up a pressure gouge to the tans and check line pressure during the 2-3 shift, but I would be willing to bet the 3-4 clutches are gone in both transmissions. Sorry I know that's not what you wanted to hear.