Unfortunately your truck is considered a "higher profile". Given the fact that your Blazer sits higher than a car you're going to have to accept the high winds and just be able to compensate quickly for it. However, you can also upgrade to a steering stabilizer and that should cut down the wheel bumpsteer you get JUST a tad.
The Pirelli's are street tires. Some of them are pretty good, just not for your truck! I personally recommend anything BFGoodrich Tires
. They have a proven track record over and over, especially in off-road racing for their durability. Sandman likes the Cooper SST's so there's another option. It all comes down to personal preference.
Firestone's quality is as cheap as their tires. My dad had a set of stock Bridgestones on his 'Yota and he put a serious gash in them just doing dirt road driving on the way to our racing checkpoint. Plus, as others have mentioned, Firestone/Bridgestone is sort of persona non-grata...
The track width is too narrow? Has he ever seen a Ford Ranger? Puhleeze... Compared to what? A full-size? Your track width is fine. It's the axles and a-arm that can stand the improvement. Depending on the type of regular driving you do should determine what upgrades you plan on making. You could go with a Limited-Slip Differential, like most stock Chevy's have and that should get you through most of what you need, unless you go rock-crawling on a regular basis, and will help greatly to keep tire wear and handling problems on your way to work on the freeway/roads. I upgraded my worthless stock tires to Bilsteins. A little pricey, but if you have a stock lift (meaning no suspension), I think they are the way to go. A little stiff but VERY responsive. I've had RS9000's on my other trucks and I'll never get them again, as I like to do a little desert pre-runner and they tend to fade very fast at speed. If you do low speed stuff they should handle quite well.
I used to live in the Worchester area. A little town called Whitinsville. Do you know where that is? Most people don't! Unfortunately for this post I was in the 2nd through 5th grade there, so I can't recommend any good shops! [img]/wwwthreads_images/icons/smile.gif[/img]
Hope that answered some of your questions.