Hi, I have a 2007 GMC Sierra Classic with the 4.8L V8 and the 4L60E tranny with 80K miles. A couple weeks ago I started to notice my trans slipping, most noticeably with the A/C on. In the past couple of days it's started to slip to the point where I downshift into 3rd when I hit an overpass on the interstate with the cruise set at 70 MPH. I've done some research and it seems the shift solenoids are a common problem on the 4L60E, I'm just not sure if they are my problem or if I need look elsewhere for the problem. I don't mind changing parts and I love working on my truck I just hate wasting money and time on installing parts that are fine to begin with.

Any input/advice will be greatly appreciated.

 

first things first.........fluid level and condition....80k is kind of low mileage to be having problems with a 4L60E....it sounds like your lock up solinoid is to blame

 

Second thing I would check is warranty. Gm 5yr 100k powertrain started in 07. You can have a gm dealer run the vin and see what the coverage is.