What the???

[mysilverado]

Last year while pulling my 5th wheel camper the head gaskets failed on my 5.7L engine. I of course was to blame for pulling too hard and many fins on the radiator being bent over as well as a sticky thermostat. As I drove to a mechanic, I noticed that the oil pressure was fluctuating but not under 20# nor over 55#. After having the heads removed and planed and the gaskets, serpentine belt, and thermostat replaced, all seemed well. When I got home I took the time to straighten the bent fins on the radiator. I had no problems with the engine until this year's first camping trip when 15 miles down the road I could hear a slight sound of hissing or ticking from under the hood. As I slowed down to stop to check out the noise, it stopped. There was no leaking hose of oil, antifreeze, nor vacuum. Getting up to speed again it was fine until about 40 miles later when again there was the noise and with it a drop in oil pressure to 15-20# for short periods of time 5-20 seconds. This oil pressure fluctuation seems to happen at random and the slight ticking/rustling/hissing noise only when pressure is down while pulling a load. Could this be a warped head? Or a blown gasket? Oil level is not too high nor too low. I can't see that any coolant is being lost either. Could this be a bearing, rod, or seal failure? What would be the most economical way to find out. Last mechanic I went to said he couldn't fix it if it wasn't not working at the time. Is there anyone out there who can help me?