Hi, welcome to JustAnswer!. This is Ed.
Funny you'd mention the squeal!
I had exactly the same complaint a number of years ago and it WAS related to a vacuum leak that sucked so much air from the crankcase that it caused a squeal noise from the rear crank seal.
It was the intake manifold.
The lower intake gasket had sucked out and it was applying so much force to the crankcase that it caused the rear crank seal to vibrate as air was pulled past it. You may notice that the engine idle runs higher than normal or that there is an idle unevenness, but the problem is that the vacuum leak is contained below the intake manifold and transferred to the crankcase. That breaking the seal by pulling the dipstick changes the noise, it positively verifies that you have a heavily negative pressure in the crankcase. The good news?
It may be that your truck is covered by Recall RC-643-95 which exactly covers this sort of problem. You'd need to provide your VIN to me online for checking (which does become public domain) or call your local Dodge dealer to see what your recall applicability is. I'd be happy to run your numbers if you send me the last 8 digits of your VIN (but remember it can be accessed forever online). There are close to a dozen recalls listed for this truck and engine combo, so others may still be waiting.
Despite this being a free factory fix, PLEASE rate my diagnosis favorably, as this is the only way I can be compensated for my time. It'll save you hundreds in diagnostics and repair costs.