Here is my input on this.
LONG post but may be worth the reading.
A good shift kit will help a trans live as it will reduce friction on the bands/clutches that can cause glazing and heat warpage to the steels.
The B&M,TCI,etc are pretty simple in their design.
They let more fluid pressure rise so the parts slip less and engage faster.
The problem with them is that they dont really make anything work better... just faster.
In a normal driving mode it dosent take much to get the bands/clutches to engage and hold a vehicle in gear.
Think of it like a set of brake pads for example.
You wouldent want to slam on the brakes everytime you stop as it can wear out the pads fast and cause extra heat buildup in the rotors and that can warp them.
You only need to stop really fast once and a while.
The same goes for a trans in the oppisite effect.
You only need full holding power on the bands/clutches at wide open throttle.
Other wise your just putting extra wear on the trans.
The lining on the clutches and bands/steels are much the same as a set of brake pads/rotors.
Trans-go makes the best shift improver kit out hands down.
Instead of applying a lot of pressure at everyshift the trans-go kits try to only apply enough pressure to hold what is needed without a harsh ingagement.
Kinda like pushing the brakes down just hard enough to stop the car without locking them down.
But at full throttle (when it is needed to hold full power) they allow enough line pressure to hold it and you get the nice tire chirping shift we all love (except the U joints but that is another story
)
Im not saying that the B&M/TCI kits are bad though.
I have used them on many cars with good things to say about them.
Truth is they work!
But I can do the same thing to any trans with a small set of springs and a small drill bit to make the holes bigger on the separator plate for about 5$ instead of 25-40$ they charge for a kit.
I dont think you can beat a transgo kit as they have many hours of R&D on their kits, to see what will hold the most power & live the longest at the same time.
Most people will be fine with a B&M/TCI kit as long as they change their fluid.
I used to build auto transmissions for a living and I have seen what a trans-go and the B&M type shift kits do to the trans.
The trans-go kits always have less muck (small parts of the friction plates/clutches kind like brake dust) in the pan when you drop them a year later to do a filter/fluid change.
As I said the B&M style will work fine so long as you change the fluid every so often.
But then again you will always hear about someone that has a trans with 150K on it and has never had the fluid changed.
Well I know people that go 15,000 -20,000miles on a oil change too but thats not smart either.
Fact is that B&M style kits are cheaper but they put a little more wear on the trans and you will need to change the fluid every so often to keep the fluid clean and doing its job right.
The trans-go kits put a little less wear on the trans but they will still need the fluid changed just not quite as often.
Basic rule of thumb is when the fluid on a transmission dipstick is kinda brown looking and burnt smelling its time to change that fluid!
I hope this helps with anyone looking for a shiftkit.
Not badmouthing any brand and in fact I use a B&M style kit in my truck but I change my trans fluid every 30,000 miles.