2000 Ford F150 egr valuve

ok i have a 2000 ford f 150 and iv ben having problems 1st it was sylinder 7 misfiring so i went ahead and changed all 8 spark plugs and the service light went off fev days later it came back on and we tested it and it was cylinder 7 and the egr flow and i was told to clean it out with coat hanger and cleaner so we did and i got a new coil for the spark plug and the egr im still haveing BIG problems with iv cleaned it and the service light keeps cummin on after so long and my fuel miliage have gone to crap i youst to get about 400 miles to a tank of gas with a 25 gal tank now i get 100 miles to a half a tank should i buy a new egrwhat else can i do

thanks
Bryan