got a sputter

ok I tried this before but got no response hopefully this time I will. ok I got a 1991 4x4 s-10 blazer and havn't had anyproblems with it..untill now.. when it idles it sputters real bad and when I hit the gas it sputers like a mother and takes off very slow and than when I get to about 65-70 mph it doesn't like to excelerate anymore now I'm thinkin its think injecters but I aint sure so if you have had this problem before and know how to fix it or if you just know what it is from could ya let me know cause its really startin to bug me thanks in advance

1.) Tuneup w/ Fuel Filter

2.) Exhaust Back Pressure Test to check for a clogged CAT.

thanks

Check Engine light on?