2001 CHEVY SILVERADO 5.3 Z71 The truck uses 1 gal of antifreeze

Because revving the motor makes the oil pump spin faster and therefore increases pressure. It should be stable and within specs when you are at cruising speed.

Transfer Case
NVG 236 and 246 Auto-Trak II Fluid Gm P/N 12378508 NVG 261 and 263 Manual Transmission Fluid GM P/N 88861800

Were is oil sending unit on a 1998 chevy z71 silverado 5.7 liter? Oil pressure is dropping to 1/8 of gauge

First- When was the last time you checked it & it was full?
Second- Is a lot missing (1/2 gallon)?
Third- check the oil dipstick for any antifreeze in there or any white smoke from the exhaust,that would indicate a possible head gasket leak.
Fourth- Do you smell antifreeze inside the truck? Look for a small leak under the glove box in the dashboard for the heater core.
Hope this helps

what is the normal reading?
it may have to do with the viscosity of the oil if it is thicker the pressue will show higher if thinner then it will show lower.

if it is showing extreamly high and does not drop once the engine has warmed up then your oil or sump filters maybe blocked.

I hope this was useful.

check your ujoints may have a bad one.

OIL IS LEAKING BY VALVE GUIDES.BURNING WITH FUEL OR REAR MAIN SEAL LEAKING. CHECK AROUND FLYWHEEL AREA TO THE OIL PAN .ALSO IF FRONT CRANK TIMING COVER SEAL LEAKS IT WILL LEAK WILL CAR IN MOTION.OIL WILL LEAK ALONG THE HIGH WAY YOU WILL LOSE OIL THAT WAY.

The freeze plug you replaced was due to rust or was it pushed out by freezing temperature? These plugs are not designed to protect the engine block from cracking during freezing temperatures, they are there to remove the sand from the block after casting it. I would drain your system completely and flush out the radiator thouroughly and fill with plain water, then run the engine and see if oil gets in the water, if it does and the plug was out due to freeze, then your block is probably cracked, although you could just have a head gasket leak. Oil pressure (40psi) is higher then water pressure (17psi), so getting oil in the water is always more prominent than the other way around. Flush out the system and let me know if oil returns to the water, hope this helps

i would try to flush the cooling system completely
if I had to guess someone put stop leak in it when the freeze plug started leaking
also check the oil to make sure there is no water in the oil

There should be a tag on the rear that tells you the weight. It is probably sythetic oil. If there is no tag, call any Chevy dealer, ask for service dept. and they will tell you.