2007 Tahoe Transmission Issue

[OWSI]

I had a big issue yesterday while traveling for the Christmas holiday. Running about 70 mph on the interstate in TN/KY. When applying light to medium throttle I would feel a "bucking" sensation. Very much like the engine had developed a miss. Kicking the throttle down and accelerating, I felt nothing. Return to normal cruise and the bucking would start again. No issues whatsoever with shifting and no slipping sensation either. No check engine light. I had to drive it about 160 miles like this to reach my destination. Pulled off the interstate and into a parking lot for a minute. Came back out and started driving down a rural road and the 1-2 shift was slooowwwww and lazy. Then it starts giving me a lot of slipping. Could not get 3rd or 4th gear to act normally. Would either slip like it was not in gear at all or grab and go fine and then slip badfly again like it was in neutral. Only had to go a few more mile this way to get to mom's house. Reverse works ok and first seemed to be ok until it had to shift. All messed up after that. Had it towed to AAMco for diagnostics and probably some kind of repair which they'll probably start Tuesday after Xmas. This doesn't feel like a clutch issue in the trans. It's like the electronics can't get it into a gear or keep it in one. What I really can't figure out is why it never felt like it was slipping for 160 miles on the interstate and then was nothing but that after shutting it off for a minute and coming back to it. I suppose the bucking feeeling could have been some sort of slip and no slip, kind of like someone was playing a rapid fire torque converter lock/unlock. Don't know and it's very hard to describe this accurately. In the interest of not damaging anything further than it might already be, I didn't go out and do a full round of trying to figure something out and document when it would do slipping/gear changes, etc. I just had it towed to the transmission shop and was thankful I got where I was going and wasn't stranded somewhere.
The vehicle has 134k on it and the trans was serviced at around 112k with new fluid and filter by the dealer. It has never given me any problem whatsoever. I drove the vehicle on the interstates for almost 3 hours before this issue started with not the slightest indication of a problem. The trans fluid is still full and doesn't look or smell bad. The GM at the trans shop said there are 7 solenoids/modules on this transmission and it could be one of them or an internal failure. Won't know til they get it on a scanner. Even after the slipping and goofy gear changes started, I still never got a check engine light or any other instrument panel indication of a problem. Engine temp stayed normal and the trans temp on the interstate was running its normal 180 degrees. When I say slipping on this, it was't like it felt like it was in gear and the revs were just higher than normal. It felt like it was in neutral and you could rev it to the moon and back with no change in vehicle speed. I'm at a loss as to what this could be other than maybe debris in the valve body or something. Thoughts?

 

[lamerem]

When you say they did a filter and fluid change, did you verify this? Many dealers call it a transmission service, but it is really a flush. I have found in my dealings with GM dealers is they will do everything they can to not crack open the trans. They are now even going to the extreme of calling the filters "lifetime" filters. Those that might read this may not know but a flush machine pushes fluid in a reverse manner through the filter. In essence this cleans out the filter by pushing contaminants back out the way they came in. The downside is that this all goes back through the transmission. While the majority gets out a lot still remains in the transmission.

Now, I only bring this up because I had a transmission serviced at a local GM dealer. The service writer told me it was a filter and fluid replacement. When the truck came out i asked for the filter to be cut in half so I could view it's contents. They provided a filter for my viewing pleasure. What they didn't know is that up until that morning I was going to do it my self, then it snowed. So I questioned the filter and was assured that it was the right filter. I gracefully walked over to the truck and pulled out the GM filter that I purchased from their parts department 2 weeks prior. Guess what...no match. They were speechless. This is when they owned up to the fact that GM dealers are advised to flush with a reverse fluid pressure machine rather than the full service. Why might you ask? They charge the same amount of money, but it costs them less than 1/3. It is more profitable for them, and more risky for us. I demanded my truck be put back on the rack and the pan dropped. I stood within watching distance and observed them using the filter I bought (which the refunded for the trouble, they also refunded the service costs) and fill with fresh fluid.

Moral of the story, I DO NOT TRUST DEALERS. Service departments are the cash cows, it's how they stay in business. They are no different than any other retail location. They tell you what you want to hear, sell you what they can and send you on your way. If you come back, they blame your car or driving habits.

 

[kbuskill]

My guess would be torque converter.

 

[OWSI]

I can say for certain that the fluid/filter replacement were done. It ended up that the pan gasket was overtightened during the process and had to be redone by the dealer a month or two later. No cost to me. The dealer is reputable which I understand not all are. A torque converter issue is possible, especially given the way it acted on the highway. I guess I will find out in a couple days when the shop finally gets it on a scanner. I am just hoping it doesn't turn into a full rebuild as obviously, that would be much more expensive than a solenoid or converter replacement. Hoping for the best. Thanks for the replies