I'm running one. Doesn't do so much on shifts, but rather, overall system pressure. It holds better once shifted. Of course, if the system pressures are increased, there will also be a slight change in shift quality also, but if that is your entire goal, you'll likely be a bit disapointed. A Corvette servo will give bigger gains in shift speed, especially the 1-2 shift that seems to lag so much on the 4L60E.
It is a good mod for the low bucks it costs, though. I'd do one the first time the pan is off for a filter change, as it takes no further dissasembly, except to pull the actual boost valve out of the front pump with a snap ring pliers.
What you'll need to accomplish the part swap is a GOOD long-nosed snap ring pliers of the correct size (the holes are about medium size -- consistent with any snap ring in the hardware store with about a 1/2-3/4" diameter -- if you want to size up the tool before you start), a smallish screwdriver (just in case you need to hold the valve in position while you get the snap ring in or out), a small light to see stuff, and sometimes a needle nose pliers helps.
Otherwise, it is very simple. Remove snap ring; remove old valve and spring; install spring on new valve; push back into bore; re-install snap ring. The valve is located in the front pump at the very front of the transmission case (directly inside the front edge of the gasket rail) and slightly to the left if you are laying under the transmission with your head toward the engine. It is up in its hole about 3/4" or so. The boost valve that comes out is just an aluminum plug with a small bump on it. Easy to see, easy to swap, except that once in a while you wish for another hand.
Do you have a tune yet? If not, spend the $100 or so needed for a PCM for Less tune. That is THE best modification for the TrailVoy for the money. There, you can specify the transmission shift level from 1-3. I have a 3 setting, and it is firm, but not nasty (not like my old B&M race kits!).
If you are looking for tire-squealing shifts, get a different vehicle. NEVER going to happen unless you have the SS and do some work.