hi everyone im new but i had a qustion i have a 89 blazer full size k10 and i put headers on and not the o2 censor but haveing trouble at higher speed could i put the o2 censor in the muffler pipe

 

You definitely need to get that O2 sensor installed. It should be installed as close to the engine as possible. I would put a weld on O2 sensor bung on the collector of one of the headers. If the stock wiring is not long enough, then you can extend it or buy an extension harness pre-made.