1997 Dakota SLT 2wd 5.2

first got the truck it ran great, then it would slowly get worse and worse. the last month or so ive been chasing a misfire. ive changed coil, plugs (multiple times), wires, distributor, o2 sensors, oil sending unit, capped off evap box under bed. it threw 8 codes, 6 for misfires and 2 for o2. fixed the o2 and they went away. Found a spark plug that was cracked, so I changed it again. runs better now, but code 306 is still popping up. and occasionally a 300. I'm thinking do a compression test or I have a bad injector. I'm tired of guessing and just want it running right, any help would be appreciated. thanks

 

thanks guys, so useful around here