95 Sierra 3500 idle problems

I have a 95 sierra 4x4 with a 5.7 tbi and manual tranny. Ive only had the truck for a few months and I noticed that from in the cab it felt like the engine would miss and give a little shake or kick that you can feel in the cab when idling. The tach was pretty steady right around 600rpm so I didnt think it was anything serious and decided just to check a few things and do some basic maint since I wasnt sure what was done prior to me buying it. I replaced the plugs,cables,cap and rotor. I had the alternator and battery tested and both were bad so I replaced them also. The truck had a KN air filter in it when I bought it. So instead of buying a new one because it was dirty I bought the KN cleaning kit. I followed the instuctions and cleaned and reoiled it and let it set over night to dry. I put it in the next day thinking all I had done might fix the prob if something was wrong but nothing changed. After a few days my idle got worse when I started the truck and when I checked the air filter again the oil from the filter had coated in my throttle body. I used throttle body cleaner and cleaned all of the filter oil off that I could see and threw that piece of s!#t K&N filter away and replaced it. What is going on now is an elevated idle thats about 1500rpm when I first start it (which sometimes starts right away and other times takes a few more cranks) and takes a few minutes to drop if I drive right away or let it sit and idle. Also the missing feeling is still going on. My questions are: is the missing feeling normal since the tach looks to be steady? and is there anything that I should check that the oil from the filter might have messed up? I would appreciate any suggestions. Also I have another thread about a 4x4 issue I have on the same truck so check that out also.