Hello everyone, new member here. I'm having a transmission issue that I was hoping to get some advice on. I looked through the common 4L60e problems thread, and nothing seemed to quite match up with my experience, so I wanted to ask the experts here.

I just purchased a 1997 Chevrolet K1500 Z71 4x4 (Vortec 350, 4L60E, 14 bolt) with 150k miles about two weeks ago. I feel the truck has been very well taken care of mechanically, the interior is practically immaculate and the exterior is also in great shape. When I test drove it prior to buying it, it drove great and stopped great. In the last 3-4 days, it has been very cold in my area (and it got cold all of a sudden). Since the cold weather started, my transmission has been acting strange in the mornings, and occasionally if it sits long enough for the engine/transmission to get cold enough again. When I first put it into D after a cold start, it idle-rolls much faster than usual with my foot off the brake. When I give it any gas, it sounds like a very large fan has been turned on in the engine compartment, and it feels like there may be some slippage. It doesn't seem to shift gears during this. It does this for a very short time, and then it goes into gear and behaves normally for the rest of the time I drive. It goes into all gears fine, and the loud "fan" noise is gone. I did a hot fluid check and the level is good, and the fluid does not look burnt at all.

Also, yesterday after I had been driving for a few minutes, while stopped at a stoplight, I felt a slight shudder in the truck. The RPM did not look like it was fluctuating at all, and when I pulled away from the light it drove normally. When I got to my destination, I held it with the brakes in my parking spot (in Drive) hoping to replicate the shudder, but it did not do it again. I tried to replicate the issue again last night and this morning with no success. I am unsure if this issue is related, but I wanted to mention it in case it is.

Any information about this issue (issues) would be greatly appreciated, and I can answer any questions if needed for diagnostic purposes. Thank you

 

Some of your symptoms sound like the torque converter clutch is dragging a bit.
Never heard anyone report that their trans/converter sound like a "big fan".
I would start by scanning for engine codes, verifying the TPS goes from 0% to near 100% and to determine where the fan noise is coming from.

 

Back in the day of the clutch fan, you could mistake it for a transmission slipping. The fan wouldn't work right and it sounded like a (big fan) and "a lot of people" would think it was the transmission slipping. You having 150K on your truck could be as simple as low fluid, maybe a leak, you'll have to check it. When it gets cold a lot of transmission problems show themselves. If it was slipping you'd get an 1870 code. Just a few things to look at.

 

I had the local Autozone scan for codes, and they found none. I should add that the check engine light has never come on for me.

I do have a clutch fan (instead of electric).

Since there are no error codes, i'll next try to test the TPS. I'm wondering if it will seem fine now, vs on a cold startup when i have my symptoms.

 

Sometimes when they get old, the seals get hard, the cold makes it worse-as the trans gets warm, the seals get a little softer, and start holding pressure.
If that's the case, time for a rebuild