My 2.8L LT ECU is done so I am replacing it. If I replace my ECU with a junkyard\ebay one, must it be reprogrammed for my vehicle (VIN, etc.)? Will only an LT ECU be compatible, or will another 2.8L engine ECU work too?

Odds are it will come with no memcal. You need to swap in the same from your old ECU.

Helpful instructions may be in stickies.