check engine light toruble, rough idle

I have a 98 chevy c1500 and the check engine light is on I took it to a shop and they
scaned the code and it said it was the cam and crank shaft position sensor. so I
replaced both of them now the light is back on and I had it checked again and now it
says it is just the crankshaft positon censor. the light goes on and off all the time and
if I leave the car setting over night and try to start it the next day it has a very rough
idle it comes so close to stalling its not even funny. Then when I put it in drive and
press the gas it does not have much power at all it will run like crap for about 15 min.
then its fine and acts if there is no problem at all I have no clue what it is I replaced
the spark plugs and wires and distrubutor cap and changed the oil and air filter. Also it
feels like it has a small miss to it. Any help is despratly appreciated thanks.