Ok, History: Swappped out a tired,knocking 350 TBI for someone. I still have the truck at my shop. It is a friend of a friend. He brought me a J/Y motor which I do not like doing. Anyway, I had to extract the studs in the manifold to y-pipe cause they broke (rusted). He also told me that someone had tried to get the 02 out and could not. So I figured while I had the manifolds off I would heat it up and get it out. He got a new one a couple of days later and the motor was already in the truck. I was wondering to myself, why the other person was trying to get the 02 out...hmmm. So I tried putting the new 02 in the manifold while it was in the truck. When I heated the manifold near the 02 I must have distored the threads a little. So the new 02 would not screw in at all. Now I was kinda heated cause I am doing a favor and not really making any money and a new tap for these are 50.00. So I was able to screw the old O2 in. Also while I had the dist out, I put in a new pick-up, module, cap, rotor and wires (all GM parts). I got the truck running yesterday and set the timing (in timing mode). Anyway I drove it for a while today and when fully warmed up it stumbles and hesitates off idle. I finally was able to get a code and it is code 45. So I checked in a How to repair and Mod. chevy F/I. I have not had time yet to hook up a DVOM to the o2 sensor circut at the ECM. This truck was not taken care of at all. I do not know if the fuel filter has been changed. I will ask the customer tomorrow and I will also ask him if he had a C/E light and hesitation. I bet he says he never had a prob. Any help would be appreciated. T.J.