You'd need a lawyer
and a good engineer. Iron never lies. If the shifter caused the failure there would be evidence to support it. If the shifter didn't cause the failure that evidence would be present also.
Warranty is supposed to cover manufacturer and material defects. Material defects are clearly identifiable when a part is analyzed by a competent person. Workmanship is a little tougher to see, but evidence is still present. I'm not sure what it would cost to have a material engineer look at the parts, but I know that a couple of my colleagues (who have Chev's) have already had problems (go figure

) and have caught the dealer trying to replace parts that are not damaged and tried to give them a run around. Luckily it never worked.
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White 1995 Mustang GT
Dynomax Cat-Back, Offroad H-pipe, K&N Filters w/o Air Silencer
My 1995 Mustang GT