2002 chevy silverado 2500hd 6.0 4wd

Question

Check engine light blinks on  and off at about 60 mph. Code p0300.

Answer 1

P0300 Random misfire

Clean the code , and test at idle, if the misfire event only occurs at high speed , a exhaust back pressure test should be performed, At highway speed , the suspected area to look for are plugged exhaust system