what should i do to my stock 99 blazer 4.3 l so that i can off road?

Well, you're probably going to need a lift + bigger tires. Although, I DO know one crazy guy in a Cherokee that runs it stock on the trails...but I wouldn't recommend it. I'd suggest making sure you have proper tow points as well...

i hav a stock 98 blazer 4x4....all i hav done is an intake and i run it on the trails....then again i got stuck in mud and another dude had to pull me out...i m in the market for bigger and better tires now...make sure you hav hooks to tie a tie rope to...a toe rope would help also

I've taken my Blazer on some off-roading trips and it is stock. Given I didn't take it through any real thick slick mud, so I can't say how it would do in bad mud. I did go up and down some pretty steep hills without any problem though, I was fairly suprised at how good it would climb.

I have a 2000 4 door...4wdr...never had a problem doing anything with it....except maybe swim....eeeek!

You don't need to do anything to it. Bring a friend and a tow strap. Go wheeling.
The best mod is better tires. Start there.

Couple of tips though, never attach the tow strap to your bumper. In back wrap it around the frame (or install a tow hook), up front use the factory tow hook.

i had an 88 s-10 blazer all stock with bf good rich all terrane t/a's and sunk it so i coud not see any of the tires at all and it crawld right out

i have a 2dr highlifter 4wd. i have been going through some pretty sloppy stuff in 2wd with no real problems. got stuck once. thats how i found out my 4wd didnt work. its gettin fixed today tho. cant wait.

I've got an 87 s10. all Ive done to it is put some 30's on it and it's been able to handle some level 5 trails.