Dropped RPMs

My RPMs just started to drop that I almost stall when stopped and since the weekend when I'm driving the car will drag for a split second every few minutes (almost like I ran out of gas) I just got the heat riser fixed Wed. would this have anything to do with it? If not anyone have any idea?

I am not sure if this is your problem or not but I had something similar to this happen to me and it ended up being my fuel pump that died. Also when was the last time you changed your fuel filter? I know that is something basic but something to think about.