OK... I've got a 06 Impala with the 3.9 v6 and 4 speed auto with 153xxx miles... I took it on vacation this weekend and noticed I was getting a small vibration will accelerating down the interstate... got to where I was heading and into some stop-and-go traffic... went to take off and it revved slightly before catching suddenly then felt like it slipped a few times before taking off... fluids are fine and what not... It is becoming more frequent since this happened... is it time for a new trans? Or is there anything else I can try? The place I bought my tires from reminds me to flush the trans every time I go in there but I was always told (by my grandfather) flushing usually does more harm than good... also, if I'm looking at a new trans, is there anyway I can use the newer impala's 6speed auto instead of the 4speed auto that's in it? Thanks in advanced!
Good ole 4T65E transmission. Have you checked the transmission fluid level recently? Sometimes small leaks can turn into bigger issues later down the road. If you are low on ATF, I suggest you re-fill it as soon as possible and find out where it's leaking from. If the fluid is full, what is the color of it? It should be a nice deep red\purple color. If it starts to turn brown, or even starts to smell burnt, odds are the clutches or are burning, or the torque converter clutch is starting to come apart. Usually once either starts happening, it will only get worse over time. As for the vibration that you say you felt while driving on the interstate; was it more of a vibration under constant throttle above 50 mph, or during quick acceleration that would be involved with passing another vehicle?
Do you have a check engine light on at all? If you do, they are pretty notorious for the "P1811-Max Adapt & Long Shift" code, especially at higher mileage. If you have the P1811 code, it's been my experience that an overhaul at a reputable transmission shop or a re-manufactured unit is probably the best option.
As for flushing the transmission or changing the fluid & filter, if you're already having problems, save your money. It may actually do more harm than good. I would only say change the fluid & filter if you do it at regular intervals (every 15-20k miles for example), and do not have any current shifting-related issues.
I also don't think that installing the new 6 speed transmission in a 2006 Impala would really be a realistic option. I'm also positive that the ECM would have to be chipped\replaced & I don't even know if that would really be an option. Usually changing transmission types doesn't ever go smoothly in the era of computer-controlled vehicles. For example, even though the 4T65E transmission has been used in Chevy Impalas from 2000-2008, you would not be able to use a transmission from a 2007 Impala, or a 2005 Impala with the 3.9L engine. They usually change things like plug connections, electrical sensors, etc. that won't be recognized by the car's computer system without modification. It's unfortunate, but that's just whats going on now-days with cars.