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I was wondering how many miles did you have on your truckbefore you had to have the 4L60 auto trans worked on. The reason for this question is that at 31kthe one of the clutch packs for first gear failed. Lucky for me it was underwarranty. Now at 86k I’m noticing thatthe trans slips when going on the freeway. The engine is at 2400 RPM, you givea little gas to maintain speed and the trans slips a little, the RPM’s go upabout 100 or so then the torque converter locks back up and the rpm goes backto where it was. It’s very subtle but noticeable.This happens, or I notice it, when driving empty and not towing. I don't ever remember this happening before. Could this be the beginning of some troubleor is already too late. I have the transserviced at about 30k intervals, 31K when they worked on it and at 62k beforegoing on a 4700 mile road trip.
It sounds to me like your transmission is working as designed. The torque converter, when unlocked, allows slip between the engine and transmission. When you apply more throttle the converter will sometimes unlock to provide more power. When this happens the RPMs will increase, and is completely normal.
How does your transmission fluid look? If it's actually slipping it will be black!
Sorry about the trans designation. I was going off memory and misquoted musthave been thinking of my friend’s truck. I’ll check the fluid color today, though I did check the level a fewweeks ago, but didn’t notice the color being off or not normal. I guess I never noticed it before but it doesseem like it’s acting different. Maybe I’vebeen driving too many different cars lately and am getting a little paranoid.
No big deal, your post just confused us, that's all! If I remember tonight I'll take a video of my truck doing what I think you're describing and post it here.