This isn't behind an LS motor, but it is a 4L60E in my 1995 K2500 truck.

I picked it up a few days ago and it was running and driving fine, but now I have a problem with it slipping on the 2-3 shift pretty bad. Even at part throttle. If you back off the throttle it will grip and then be fine. All other gears are fine, even if the shifts are super soft.

The truck has done 128k miles and the transmission is totally stock and from what I can see looks like it's never been touched.

I plan on pulling the pan off in the next couple of weeks and having a quick look inside.

I've rebuilt a few of these transmissions before and it looks like I might need to do this one at some point soon?

Anyone have any thoughts?

On a side note - is the 2wd and 4wd transmission the same with the exception of the tail shaft?

 

If it is slipping even at "part throttle", then the 3-4 clutches are just about gone. If the 1-2 shift has not changed at all, then the line pressure (line rise) still sounds ok. If it has changed, put a 0-300 psi. gauge on it and get some readings. Then I would drop the pan immediately and see if there is any clutch material in the pan. In the meantime "do not" let it slip, get out of the throttle immediately, as this will finish off the 3-4 clutches quick.

 

That's what I thought would be the case to be honest.

The 1-2 shift is fine it's only the 2-3 shift that slips.

I'll have to drop the transmission out and overhaul it sooner rather than later then.