2001 Dodge Stratus Sputter in low gear after warmed up with

My car printed out code for mis fire a month or so ago and at this time the car was running great in all conditions. However I immediately took it to my mechanic due we did a tune up spark plugs, wires, distrib. Etc. Continued to run great within a week a mis fire code came up again. Started occassionally not idling right after warmed up. Decided due to mileage etc. Would replace fuel pump, filter etc. Replaced all of the above and runs great at high speed, but in lower gear/idle only after warm up it seems to act like it was getting to much fuel (with the air conditioning on and wants to sputter die out; if you let up on fule/acceleration and turn air off it is o.K, back to mechanic who says the water? Temp is not reading acurately so also replaced temp sensor, still doing it, runs much better also when tank is completely full. Now the check engine light came on and code is cad coverter, meanwhile performance is not dragging and running fine? Any ideas what to check for next. I am in the kern county area of California and was just notified that may have received contaminated gas (probably what cause the fuel pump/filter to be replaced) could there be more?