Oil pressure Gauge and fuel gauge wacked out!!!
 

OK so here is my problem. I have a 2001 dually 24v dodge Cummins pickup with 331k miles and recently I have noticed something weird with these few gauges. First I noticed my oil pressure gauge running at 40 pounds NOT running! So I went wtf and went after a new sender like 80 bucks later I went to start it and with the key on and engine not running the 40 pounds appeared again! So I just said the heck with this crap and got me a mechanical one. So after I got that thing installed with the old sender connector unplugged it still read 40 pounds with the engine not running!!! So I just went on with it thinking a electrical problem and I left it alone. So a week passes and I'm Hauling a 6.0 back to the shop and not bucking any wind or pulling any sorts of Hills (I live in the plains of Kansas) I get these huge clouds of random black smoke come screaming out my stacks and I never even touched the throttle! And then everything went back to normal and I continued on Hauling that piece of junk iron to the shop. Well on the way home the same thing happens. I get backto town and my fuel gauge freaks out jumping from half of a tank to empty and to full and well all over hell so I hurry to the diesel pumps to get fuel and only took six gallons. Oh and the little trip I made I averaged 9 miles to the gallon where usually it gets fifteen. My buddy told me that is ecm failure. Is it possible?

I would say ecm failure is definately a good possibility but, as of yet i wouldn't rule out other electrical gremlins till you've dug a bit deeper, hard to tell from that info.

Would the ecm cause the oil pressure issue even with a mechanical gauge tho, since its not hooked in any way shape or form to the factory system ?

Get a code scanner from an auto parts store and check it for codes.