Transmission issues

[Love0126]

Hi,

I have a strange question.  I picked up a 2005 GMC Savana with the 5.3l, and about once per week, I will get a strange 1-2 upshift. It comes off the line from a stop with the engine revving higher than normal, almost like it's half in gear.  Then it seems to catch and shift like normal.  I have tried engine braking in the parking lot and it doesn't seem to be slipping.  Fluid is topped off and pinkish.  Any ideas on what could be causing it?  No codes.

[C/K Man]

1500?  probably has a 4L60 transmission.  Sounds like maybe the forward clutch is slipping, might not set a code until it starts to happen more often.  Maybe oil pressure in the transmission is low.  Sometimes you have to put some more miles on and wait and see if it sets a code.

[Love0126]

That's kind of what I was thinking too.  It is a 1500 with the 4L60e.  I will double check there are no codes with my Tech2 and post if anything has changed since the last time.  If the tranny gives up the ghost, I kind of want to swap an 8.1L or a Duramax in here.  . I dislike the lack of torque that the 5.3L has down low.  

[carkhz316]

If it is indeed a 4L60 (I know some 2500/3500 vans come with the 4L80), it is most likely the 2-4 band that is worn and slipping. The forward clutch wouldn't be a culprit as it comes on in 1st gear and stays applied through all the gears. The only mechanical change from first to second gear is the application of the band, which stops the input drum and sunshell from turning.