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You may as well get a new cat back muffler. It'll give you a nicer sound, and better performance. Probably better mileage as well. You can probably do this job yourself, unless the cat was welded on.
I'd recomend a tire that I've heard of, like BF goodrich, All Terrains, or something along that line. Then if you get a flat they'll fix it on waranyt in 90% of the tire stores without any hastle.
Stock size is 235/75-15. You can get as big as 30"x9.5"x15. These tires are about 1" taller and 1/2 inch wider.
don't know much about ABS, so I'll pass on that 1.
The Library probably has a manual for you to look at, but with the amount of money that you've already spent on it you should just buy 1. Walmart should have them in the US.