2000 blazer 4wd, 4.3l low oil pressure? HELP!

My wifes 2000 blazer 4.3l v6, 4wd has 170,00 + miles on it. My question is regarding the oil pressure. What shouild the oil pressure be at highway speeds of 60-70 mph. The pressure goes up to just over 40 at those speeds but when she stops or puts on the brakes it goes down to 20-25. Is it time for a new oil pump or is the motor on it's last leg?

ALSO I CHANGED THE OIL A FEW DAYS AGO, THERE ARE NO LEAKS AND THE OIL LEVEL IS NOT LOW.

My wifes 2000 blazer 4.3l v6, 4wd has 170,00 + miles on it. My question is regarding the oil pressure. What shouild the oil pressure be at highway speeds of 60-70 mph. The pressure goes up to just over 40 at those speeds but when she stops or puts on the brakes it goes down to 20-25. Is it time for a new oil pump or is the motor on it's last leg?

ALSO I CHANGED THE OIL A FEW DAYS AGO, THERE ARE NO LEAKS AND THE OIL LEVEL IS NOT LOW.

It is well within factory specs.

Before you go throwing parts at it check the actual pressure with a oil pressure test gauge.
Post back readings.

If the test gauge reading does not match the dash gauge replace oil sending unit.
And retest.

Minimum oil pressure specs for 2000 4.3 V6 with engine hot.

1k RPM 6 lbs.
2K RPM 18 lbs.
4K rpm 25 lbs.

Agreed, my oil pressure drops at idle when it is hot but is well within spec so I ignore it.

Just about all gm engines run between 20 to 40 psi, 20 when at low rpm is normal.