1998 Dodge Ram Check engine light + noise

I recently replaced the heads on my 2500 because it had a hole burnt thru the exhaust valve # 8 cylinder. The truck ran really great for 1000 miles and then the CEL came on and the codes were for misfire detected on cylinders # 5 and 6, I was baffled because the engine was running really awesome at the time except a very little stammering at idle that it has had since it was new. As time progressed a noise was noticeable while accelerating under load that was similar to a exhaust leak, every time I have tried to locate the source I cannot here the noise in the engine compartment or from below. It also seems I need to drive a bit before I can hear it. It has gotten worse with time and I have stopped driving the truck except for times of dire need for fear something is going to be damaged badly.
I have checked the compression on # 6 cylinder and it is 135, however with a leak down test I couldn’t get it to hold air until I loosened the rocker arms no matter how I bumped the engine there seemed to be no spot that both valves were completely closed is this normal or is a possible problem in the camshaft and or valve train? Sometimes when I am driving the noise sounds like it may be a lifter or something like that. I can repair any thing that the problem may be but would like to know what it is before I start blindly taking stabs it. I used Felpro gaskets and replaced the head bolts with new Felpro bolt so I can’t hardly believe I have a blown gasket but that is the most likely candidate for a culprit I can come up with. In the mean time the idle has gotten a little rougher but my battery went dead a few times and the light resets when this happens it takes a while to come on again I will run a tank or more of gas before the light comes back on.