I would go ahead and buy some mods for your present engine if it still runs ok. These 5.0L engines last forever if you take care of them. Mine has over 120,000 miles on it now and it still runs like a new one even though I drive the hell out of it every day.
One thing you can do is a compression check to see what kind of shape the engine is in. If the compression check turns out ok and it's not burning or leaking oil and you take care of your engine it could very easily make it to 200,000+ miles.
I'd say go with a full exhaust first, then get some 4.10:1 gears if you're car is an AOD, 3.73:1's if it's a T-5.
Then get some underdrive pullies, high amp alternator, and aluminum radiator.
That would still leave some money left over for some 1.7 roller rockers, valve springs, and with a little more saving you could also get a new MAF, TB, and some injectors.
That would definately wake her up.
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