2004 RAm w/4.7 miss fire on #4

I have a 2004 Ram 1500 with a 4.7 engine. I have started to get a miss fire code on # 4 Cylinder. I swithced out the ign coil with # 2, drove the truck and miss fire code came back still on #4. I changed the plugs, first plug change since purchase, has 71k miles, they need it desperatly. Test drove truck again, missfire code came back again on same cylinder #4. Plugs were ok just well used, no carbon build up, no fuel smell present. Just heavily worn. While driving the truck at 55 mph at around 1500 rpms, you can feel the miss fire, accelerate up to about 2000 to 2500 rpms and the miss fire goes away, as soon as you get it back down to about 1500 rpm's the miss fire comes back. Any suggestions would be greatful

perform a compression test.