Bigger Tires
 

So i bought this 1995 Chevy 2500 6.5 Turbo diesel and want to put 33's on it and maybe a 2-3 in body lift, how much will this kill my mpg lol?

body lift will screw with the already marginal cooling system and i would stick with 265s because anything else bigger and your mpgs will suffer greatly

Body lift will screw with the cooling and you may have a clearance problem with the turbo. Going to 33's would probably help your fuel economy.