Depends on which gt you are talking about. A foxbody gt can weigh as low as 3000 lbs where as a 2010 gt can weigh as much as 4500 lbs.
3000 lbs.
You would have to refine your answer because they weigh different by years and model and trim level.
1964 1/2 Shleby mustang 1965 Mustang GT 1966 Mustang GT 1967 Mustang GT 1968 Mustang GT/CS 1969 Mustang Mach 1 1970 Mustang Mach 1 1971 Boss Mustang 1972 Mustang Mach 1 1973 Mustang Mach 1 1979 Mustang 1982 Mustang GT 1983 Mustang GT 1984 Mustang GT 1985 Mustang GT 1986 Mustang GT 1987 Mustang GT 1988 Mustang GT 1989 Mustang LX 1990 Mustang GT 1991 Mustang GT 1992 Mustang GT convertible 1993 Mustang GT/Saleen(possible) 1993 Mustang Cobra 1994 Mustang Cobra/GT 1995 Mustang GT 1996 Mustang Cobra 1997 Mustang Cobra 1999 Mustang Cobra 2001 Mustang GT/Cobra 2002 Saleen Mustang S-281-E/Mustang GT 2003 Mustang Cobra 2004 Mustang GT 2005 Mustang GT 2006 Mustang GT 2007 Mustang GT 2008 Mustang GT P.S. Shelby used to be the original mustang owner in the 1960s but in later years was bought out by Ford -Doug
The 2008 Ford Mustang GT has 300HP
The 2005 - 2009 Mustang GT has 300HP.
The 2008 Ford Mustang GT has 300HP
The 2008 Ford Mustang GT has 300HP
The 2005 Ford Mustang GT has 300HP
The 2001 Ford Mustang GT was rated at 260 horsepower
Ford rated the 1993 Mustang GT at 205 horsepower
The 2005 Ford Mustang GT has 300HP