Strange oil leak

[Doubeleive]

Thank you so much for your detailed response. The oil pressure sensor and valve cover gaskets were all replaced last year. We replaced I think it was called an oil cooler gasket as well... tiny little diamond shaped thing. I wonder if it's simply possible that my rear main leak has gotten worse. Either way, I'll try that and get the truck up on a lift soon and report my findings.

the bottom line is your going to have to clean it up real good first then look for fresh oil after driving it a bit.
for the rear main there is a inspection plate on the transmission bell housing, you can pop that plate off and look inside there with a flashlight and small tilting mirror that you can get at any autoparts store.
this video goes over some things to look for I would say the front seal they show leaking in the video is less common but also possible

 

[89Suburban]

valley cover

 

[Doubeleive]

valley cover

Meh, not likely

 

[mjpeterson]

Has the water pump been replaced at anytime? my 2005 started to slightly leak at the timing seal about 6 months after the wtr pmp replacement, probably due to over tightening the wtr pmp bolts?

 

[KC 2013 Tahoe]

Rear main seal leaks don't typically remain static, nor improve... would guess that's your culprit given the other repairs you've had done.