2006 Chevy silverado 6.6 hd duramax will not obtain highway speeds Maximum speed is 25 miles per hour Changed fuel and air filters, crankshaft and camshaft sensors and the fuel pressure regulator with no improvement What is the problem? Any suggestions please

 

have you tried the rail pressure relif valve? you really need to hook it up to a good scanner and check the rail pressure that will tell you alot. also will it rev up more then 2000 rpm?