Oil pressure while in 4wd

iv been searching and trying to find an answer.
i found several threads in several different places about oil pressure at idle or while driving.

right now i have about 40 when cold or warmed up and driving. about 13 at idle when warmed up.
normal right? (from what i read)

when i stop and put it in 4wd(high) oil pressure gets way low like 4-8psi:smiley-scared003:
that..cant be normal. why does it do that? extra strain? how can i fix this?
i think my winter plan is replace. oil pump,pan,filter. clean pickup. new rear main. might be leaking idk. oil is everywhere. but no leaks on the ground.
oil level is perfect and stays perfect until 3k miles for change of oil

The oil pressure should not be affected by the gear change. Your pressure reading on the dash is controlled by the PCM. I suspect that there is something happening to the BUSS signal to cause this. I suspect there is no problem at all with the engine itself