2001 Chevy 2500 4l80e trans issues

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by matt612, Feb 15, 2013.

  1. matt612

    matt612 New Member

    Hi, new to the forums. I have a 2001 Chevy suburban 2500 with the 6.0 and the 4l80e. It has almost 230k motor runs great but I am having some tranny problems. I picked it up for pretty cheap and it has had this problem since I bought it about 2k miles ago. Initially when I bought it I didn't feel anything the transmission shifted perfect through all gears, but on the way home about an hour drive after the trans began to warm up and the trans temp gauge began to register it started shifting very hard. It shifts late and hard almost always now, but occasionally it will shift perfect usually when its cold. I pull a car trailer with it and it doesn't slip or anything under normal driving conditions, I have however been able to get it to slip if I go to WOT while on the interstate. As long as I drive normal and don't floor it with the trailer and jeep hooked up it doesn't slip though, it downshifts up inclines and shifts back into overdrive with no issues except that the hard shifting. I have tried doing some research but have not found anything that sounds like what mine is doing. It almost like the computer thinks the engine is at wide open throttle and that's why it shifts so hard. Any input or help would be appreciated. I'm a poor college student, I'm hoping its fixable without rebuilding or replacing the tranny. Thanks

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    I should also add that the transmission always runs cool well below 200 degrees, it usually stays around 150 even when towing. The fluid visually looks fine, red, doesn't smell burnt at all.
  2. shibby2oo8

    shibby2oo8 Member 2 Years 100 Posts

    Im not a trans expert but the 80's have an input and output speed sensors to detect slip so my theory is it is detecting the worn clutches slipping and bumps up line pressure for faster/ tighter clutch engagement. Scan it to see what the tcm is doing, prob needs a rebuild.
  3. matt612

    matt612 New Member

    Thanks for the reply I will scan the tcm and see what it tells me. I forgot to add that it shifts fine 99% of the time until it gets hot, it usually always shifts great until the trans temp is over 125 degrees.

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