sumsemperfi

I have an 02 f150 w the 4.2 v6 and 4 spd trans w od. It has a problem starting some times it will fire up and run smooth others it will sit and crank for a few seconds then fire up. Usually when it does that it gets a real weak start then starts rubbing fine but the engine light comes on. I talked with ford about it and they said it is a mis fire cause by my Bosch platinum plugs. Said that motor doesn't work well with them. I also notice my exhaust has a gassy smell to it and my brother mentioned it could be an u2 sensor. Do I guess my question is. Will a bad u2 sensor cause these kind of problems.

Also some times when I park on a hill and set the e brake the light on the dash won't come on but the brake will set. Other times the light will come on but when I release the foot brake it will roll back wards. So is it time to change that as well?

Thanks in advance for the help.