trouble shooting P0303 miss fire code

I currently have a 2001 Tacoma V6 5VFE motor with 220 K miles on it . i recently had a P0303 code. i replaced the Ignition coil , fuel injector on #3 . the truck still did not run worth anything and was difficult to even start . i had the system ran again and got miss fires on #1 & 2 not 3 . so i have currently replaced plug wires to #2,4,6 , injectors on the same cylinders. i used injector #6 and stuck it into #1 that read miss fire. when i can get the truck started , foot on the throttle it runs smooth at 3,000 rpm , very rough below that and will not idle and simply dies. money is tight to replace coils on 1 & 5 at this time. other than a burned 02 Sensor code any ideas what i should look at next. other than theses repairs iv'e done all other engine parts are Original when i bought the truck.