I have a 97 blazer 4x4 and my ses light is on and flashes at high speeds like after 65. The codes that came up are p0143 and p0300 twice. Also when i start my truck i have to hold the key foward and wait for it to start. Where should i start with the misfire. Is it just plugs or am i gunna have to change the dusty cap and rotor?

 

if you're doing it yourself-that is a good place to start-especially if they haven't been done in awhile. Jerry

 

The fact that the light is flashing indicates a potentially damaging misfire. Check these threads:
P0143 Explained
P030x Explained (x=0,1,2,3,4,5,6)
The dreaded P0300 CAUTION LONG POST