Big Al,
As others have stated, the shocks on the Sport Trac are probably not shot, just very poor quality. However they should be warrantied for 12 months or 12K miles? If the Ford dealer agrees that they are actually bad they should replace them under warranty and then you can determine if the replacements are any better.
If you want the upgraded shocks, ask the dealer if you buy they, will they install them for free. Since they would have have to warranty the labor to replace the original shocks. If they agree, watch that they don't add the labor charges to the price of the shocks. Otherwise you can buy the shocks and have them installed cheaper else where.
As for the warranty. The only thing that will be lost is the warranty on the shocks since they where replaced with aftermarket shocks.
If y0ou don't have the cash now, let the dealer replace the bad shocks with the OEM's under warranty, and start saving your money for some good replacements in the next few months.
...Rich