frogman386

This is my first Post. I have a 99 silverado 1500 with the magnuson radix intercooled supercharger kit (now discontinued.) It currently has 91k miles on it and is in pretty good shape. I bought it a few months ago and it has been my daily driver since. I dont have a list of everything done but I do have some paperwork and know the build was done in 2005. ISSUES: The first problem is cold starts (whether is 75 degrees out or 10.) It starts but fluctuates the idles between 500 and 8-900 for about 10 seconds then it evens out. Once its idling, its a little strange. Its not rough idling but it still fluctuates but slower than when it started. Sometimes its fine and sometimes it may rev up to about 800 for a few seconds then back down to around 500. sometimes the idle speed fluctuates more than others. I have also noticed an occasional missfire on idle. The next issue is lets say im parked and idling. I rev it up to about 3500 and let off. The rpms drop to about 200 and it almost stalls. Then it goes back to the normal idle at about 500. The last issue is under alot of throttle. I dont usually drive it hard but sometimes its fun to get on it. up above lets say 3500-4000 rpm it has a terrible missfire and does not want to rev out. Recently I do not go hard on it because of that. If im slowly giving it alot of throttle I feel like its just not smooth like it should be. I also feel like it doesnt have the power it should (dont get me wrong, it still hauls but i dont think thats all its got.) I have been scrounging forums but havent found anyone with the same set of issues im having. Ive read all about how it could be the fuel filter, MAF and other sensors, intake manifold gasket, coils and wires, injectors etc....... I know I have good fuel pressure. I can tell it definately had more power after I bought it. I forgot to mention it had been sitting for a year beforehand with occasional start ups. But not long after I got it, I got CELs for bad cats and ended up getting some nice 2.5 inch stainless steel ones that go with the dynatech headers. I also got all 4 new o2 sensors This problem was here and still is after that replacement. I have checked for vaccum leaks and wire arching and havent found anything. I currently have a CEL for PO440 Evaporative emiisions (which I dont believe is related but who knows.) If anyone has any ideas id be grateful. Thank you for reading.