Misfires and running rich?

So, it has been misfiring on almost all the cylinders. So, I changed some of the plugs and coils but that didn't change much of the problem. So, then I removed the cats which kind of helped but again not very much and now my truck is running really rich and my gas mileage has gotten pretty expensive. My truck goes up to about 20-30 kmph then starts to backfire and the welding job that was done to my exhaust wasn't very good. I don't want to buy a new truck and would like to fix this one so any help would be great.