1996 GMC C1500 engine runs and looses speed

My truck acts like it dosen't want to start, but after a few tries it cranks and runs. As i'm driving alone suddenly there is a loss of speed, then the truck stops completely. After i sit there for a few minutes it starts again and runs. I changed the spark plugs,and also the fuel filter underneath the body of the truck. That did not solve my problem. I have been told that it's possible my catalytic converter needs to be replaced. Also the oxygen sensors as well. Where are the oxygen sensors located ?

Thank You