For the oil level, be sure the checking procedure is correct. Within a minute of stopping the engine should be the plan, after it's sat, it should be somewhere around the K in the work "CHECK" I believe, but it should be high. This will vary depending on if you have regular filters, converted cans, directly mounted spin-on filters, your selection of filter for the spin-on... Follow the directions that came with the truck (TM) unless it's modified, otherwise follow the directions that come with the modification. In a pinch, figure the volume of the filters and set the running level the same as it was. (OEM capacity plus or minus any difference in the filter system volume) and learn a new mark on the stick to reflect the correct level at the correct time.
If indeed the engine is "making oil", then you have two options. Coolant or fuel. Gutta be one of the two... Coolant is easy to spot. Diesel should be spotted by smell. If you're utilizing the multi-fuel ability, all bets are off, you may or may not have a contamination that's recognizable by sight, touch, or smell.
There are two types of gauges, and two types of sending units. Mixing and matching will result in erroneous readings, but they should be consistent. A 120 pound sender with a 60 pound gauge will reflect one half of the oil pressure that is present. A sixty pound sender with a 120 pound gauge will reflect two times the pressure that is present. A failed sender or a failed gauge in any combination will be inconsistent,
A mechanical oil pressure gauge for a spot check is a very good idea at this point. At work I own plenty of "good" gauges, but for a road test where fat tubing and cumbersome gauges don't lend themselves, I keep the discount parts store "cheapie" handy. The plastic crappy tube snakes nicely through door gaskets and hood gaps (and existing holes in a deuce firewall), and can get you a reading quickly and reliably, for twenty beans or so.. (Remember, high accuracy is not the key here, a few pounds or more difference is expected. You're more looking for it to be above minimum, below maximum, pretty proportional to RPM until the relief takes over, pretty proportional to temperature (again you'll see the relief working) and above all else you are looking for your findings to be very consistent from one gauge check to the next, one day to the next, one week to the next...
If you wish to replace your electric gauge with a mechanical one permenantly, the factory air pressure gauge is suited and durable for that purpose. Just replace the electric gauge with a new air gauge, (the gauge display says only "pressure", and suitable plumbing to the oil pressure sender port in the engine.
