Rough idling
 

Last weekend I got caught in a bad snow storm pulling a camper and about mid-way through my trip my pickup started running rough. After I got the camper unhooked and driving around this last week withit still running rough pretty much I notice it a lot when the vehicle is idling and now I get about 5mpg less then what I was getting. Ive tried adding seafoam, checked the transmission and oil level and both were good also changed the air filter but still running rough. I am horrible at diagnostics so any help would be great.

Can you tell us what you have?

YES !, knowing what vehicle you have will help !

But frequent reasons are Spark Plugs and Injectors.

The most common thing for me when my truck is runing rough is the spark plugs and distributor cap.
sometimes moisture gets in and messes it all up or you get burn marks on the cap points.
I went through 2 caps before getting a new distributor. at the time i was getting 10mpg lol sucked bad.

So look under the cap, make sure your spark plug wires arent burned by the exhaust manifold.
also dirty plugs so check that out.
I did a carb swap to a 390 and the previews owner had the fuel/air screws almost all the way out. Ended up flooding my truck to the point where the plugs were so fauled i had to get new ones. then my fuel pump died so it would still run rough and it was confusing me lol.
so check them things out.

I have a 2005 silverado with a 5.3

Also the check engine light starts to blink whenever i get above 20 mph

If it is blinking, that is a catalyst damaging misfire. You need to check & see what codes you have.