Hello Everyone and Happy New Year

I searched the forums and cant find my issue, here is the problems
1995 Dodge Ram 1500 4x4 318 mag 238,000 miles

A: when truck is cold rpms 1k in neutral, when in drive at 35mph tach at 1500 release gas and rpms return too 1k
when thermostat opens rpms 1k in neutral, but when at 35mph tach at 1500 and release gas, rpms drop to below 500 too stall if you have a load on the engine such as going up a steep grade at low speed truck will actually stall out
but if i am doing 55 mph when the thermostat is open it drop to proper rpms

B: Oil Pressure, i haven't bough a manual gauge yet so i will tell you what my dash gauge is doing oil pressure usually stays steady dead center
but right now when the thermostat is closed she stays dead center but when the thermostat open if you stay a steady rpm the pressure gauge stays center but if you hit the gas and the rpms go up the oil pressure drops it still stays in the safe zone, oil pressure reflects rpms but just backwards the more rpms the less oil pressure the less rpms the more oil pressure max oil pressure though is in the middle

A. this has happened b4 just b4 time to change oil its about 200 miles shy of changing oil this time, the last time when i changed the oil the problem disappeared not loosing any oil really in the 3k miles the dipstick was maybe a 1/8th low so maybe a 1/8 to 1/4 of a quart of oil

B. oil does look blackish and smells burnt at last oil change, currently the oil does look a little blackish not the golden brown
C. dont hear any knocking pinging, engine more or less runs like a top
D. running Penzoil 10w30 high milage and fram high milage oil filter

may have a slight vacuum leak and does have a exhaust leak b4 the muffler or the muffler its self