You're kind of all over the place here. You first mention that there is something wrong with your axle/differential (AKA, pumpkin), and then move on to an engine noise that you suspect is a thrown rod or spun rod bearing.
Before driving, I would check to make sure that the differential missing the plug is full to prevent damaging the bearings in the diff while driving down the road. If you do not have any suitable gear oil, you can top it off with motor oil as a temporary fix until you get to the shop. If you have to improvise a temporary plug, I would advise NOT using paper towels, as they will not hold up long enough to get 80 miles to your local shop. As long as the surface is clean, part of an old soda can and some RTV/Silicone or duct tape would be sufficient. Absolute worst case scenario, you could stuff an old rag in the plug.
Here is a DIY on changing the diff fluid, but it will show you what plugs to remove to check/fill the differentials:
Next, up is your engine issue. Oil pressure fluctuates based on engine load (RPMs) and oil temperature. Being that you live in the mountains of Colorado, it probably getting in the low 40's to freezing temps over night, which means your engine oil is noticeably thicker upon start up. Chances are this is why your gauge is reading slightly higher than it was a few weeks ago. When the engine warms up you will probably notice that the reading on the gauge will be lower. Check the oil level by starting the engine and letting it run for a couple minutes, then shut down and check the oil level on the dipstick. You'll want to pull the dipstick, clean it, then reinsert all the back into the tube it came from, pull it back out and check your reading. If the oil is in the cross-hatched area on the dipstick you're fine. Do not overfill.
As for the noise from your engine, if it's a high pitched squeal that changes in frequency or speed when applying the throttle, it's probably a belt that's starting to show wear, however you state this was recently replaced. I would check to see what brand of belt was used, as low quality replacements can be noisier than name brands like Gates, Goodyear or even Dayco. I would also ask the shop if they checked the condition of the belt tensioner, as this component is spring loaded and is designed to maintain constant tension on the belt to prevent slipping when under load.
If you had an internal engine failure, such as a thrown rod you would hear a clanking or banging sound coming from the engine or from underneath the vehicle.
Also, don't forget to fill out your vehicle information so that we can better help you in the future.