I have a 2001 4x4 with a 4.3 that has 107K on it. In August, I had a transmission and torque converter put in. Only in the last two months or so have I had an issue - when traveling at highway speeds (55-65), it will suddenly snap out of overdrive for a second, and then go right back in. Sometimes the downshift is gentle, and sometimes it isn't so gentle (certainly not a comfortable feeling when you're on the highway, either way). It only does it intermittently (not every time I'm on the highway), and some trips it will do it 2 or 3 times, while other trips it will do it every few minutes. The fluid is fine (full and clean).

I've had people tell me that it's due to wind (that the 4.3 can't handle going up and down mountains when it's windy), but I have a hard time buying into that. I've also been told it could be the TPS. Someone else suggested that a caliper could be hanging up and sending bad signals to the speed sensors, causing the issue.

I'm curious if anyone has had experience with it and might be able to make a suggestion before I throw a ton more money at this thing. I have to note that I haven't changed the TPS, but I did front wheel hubs, bearings, and brake pads about two months ago.

 

 

When I had a real bad atf leak, it would unlock and lock the torque converter when it was low on fluid. I know you said it was full, but maybe double check.

 

Thanks for the welcome...I've skimmed around the forum a bit, and there's tons of great info here!

No lights are on. The ABS light was on before I changed the front hubs and bearings, but went off after they were replaced and hasn't come back on since. The Service Engine Soon light comes on every once in a while, but goes back off on its own and doesn't stay on for more than 10 minutes or so. I haven't noticed how much the RPMs jump because it is always unexpected and really quick...

I've checked for fluid leaks...there are no spots under where I park it, and the dipstick is still reading full (I checked it again this morning).

 

 

Just thought I'd post an update in the event that it might benefit someone else in the future.

About a week after posting this, I was driving down the highway doing about 65 when my Blazer simply shut itself off. After getting off the road and putting it in park, it started right back up and I was able to drive the remaining 100 or so miles to my destination (yes, I drive a lot) without any issues whatsoever. I replaced the TPS, and haven't had an issue since (perhaps what I was feeling wasn't actually the tranny coming out of overdrive, maybe it was just "bucking" because of a bad TPS...I can only hope). I haven't yet gone more than 50 miles in a single trip since replacing it, so I guess we will see...

 

Hope you figured it out... Welcome to the Blazer community!

 

You said that the SES light was on. Did you ever check it for codes?