I have had this 2003 gmc seirra for a while, using it as a farm truck. Today i started it and it sounded like it had a cam because of how bad of a misfire I gave it some gas and it cleared up. None of the lights on my gauge cluster were on except a blinking check engine light. it has dual exhaust and it was smoking out of the drivers side tailpipe. earlier when I had trailer hooked up trying to haul my car after it broke down it made the same sound then I gassed it, and it didn’t move until almost being floored. I have hauled a square body gmc on it without issue before and all I was hauling today was a Kia optima, so I have noticed most of my power is gone. I have had an issue recently where I will be going down the road and my parking brake light comes on then I lose almost all power for about 3 seconds. What could be the issue

 

A couple of things. One, the Flashing Check Engine Light is letting you know that unburned fuel is being dumped in one or both ot the catalytic converters and you risk melting the catalyst and destroying it.

Two, what are the OBD II diagnostic codes?

What do you mean by "...it sounded like it had a cam..." mean???

 

Have had a 2000 Sierra for over 20 years and 180k miles and had none of these problems. Only part that has failed is the fuel pump at 125k, that’s it! Have meticulously maintained this truck, and it has been the most reliable vehicle I have ever owned.