2003 dodge ram 1500 4.7l v8.
Just changed engine and trans oil. All of a sudden my oil pressure gauge started dropping to 0 and check gauge light comes on
I don't hear any engine noise. Just got this 2 days ago and nothing but problems.
How do I make sure oil is circulating thru engine and that's its not just a bad gauge or connection?

 

Hook up a mechanical gauge to verify oil pressure.

 

does the oil pressure drop to 0 when you start to come to a stop or is it a random occurance.

if it does only drop when you are coming to a stop. does it go back up after pressing on the gas

 

The gauge drops to 0 and stays there, then check gauges light comes on and cel. I dont hear any noise from engine though. I had to drive it home that way. If I pull over and shut off truck then start after a few moments the gauge may start working again. Its pretty sporadic. Seems to happen when engine gets hot or the longer Ive driven it.

EDIT***************
Just drove the kid to school which is a total of 6 miles round trip. As soon as I pulled into the parking lot the oil pressure dropped to 0 and the check gauges lights up. No engine noise though as truck sat and idled and went through parking lot. At a stop light I shut truck off a minute and started when light changed and oil pressure is back up to middle of gauge.

Drive another mile and the oil pressure goes out again. Now the CEL comes on and Im pretty sure its the same misfire on #8 cylinder.

Now one thing I notice and not sure if it could be related is the exhaust gasses stink. This exhaust has the catalytic converter on it and the idle and acceleration is rough. Im wondering if the converter is clogged and backing up fumes to the engine causing some of these issues? I know, wishful thinking right. ;-(
In any event Im going to have that exhaust changed to a single pipe and see if that helps any. Any ideas or feedback with this latest info?