Its not a severe problem. Its only a noticeable problem. One day the blazer drives good. Then one day the blazer drives great! The outside temps are the same. Ever notice that your car seems like it has better pickup with the motors cold etc in the morning cold starts?? then it gets a little lazy once it warms up? Thats the issue im having. It feels great even when warmed up then the next day i drive it,it feels like it lost some gut. Tune up related stuff is fine. Did a tune up on it back around december with all ac delco products. Even put in a new fuel pump (ac delco) back in Jan. I seafoamed the truck yesterday. Couldnt tell much of a difference. It did idle better at least. I also removed the egr and throttle body to give it a good cleaning once again. Didnt Change anything. Im starting to think the timing chains worn out. Timing is 4 advanced as its always been. Im going to take off the dis cap and turn to crank with a wrench and see how much play i have until the rotor moves today.