If you do DONT trade your GTP in. You will get killed on trade in. Sell it outright if nothing else.
I agree with Adam, its a nice car, especially the interior but IMO its not $1,000s of dollars better.
If it were a bonneville GXP or a GTO and you were a few grand off, Id say hell yeah. but not an 04 GTP. see what happens for 05. If you dont like the new ones, at least by then the 04s will have depreciated down where it might be a better situation.
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2000 GTP Coupe traded for a 2004 GTO