Oil pressure problem when starting

Install a pressure gauge and check the pressure cold and also hot.
If you have a problem with the oil pressure, it will also show when the motor is hot.
I just replaced my sending unit because my oil light turned on and would not go off.
The problem was trying to find a good sending unit.

1)I try a new sending unit that i have in my garage \\\ no good
2)I try a old unit i have on the self \\ no good
3)I try my brothers 340 dart sending unit and it worked so i new my oil pump was still good.
4)The next day i go to advanced auto and by a new sending unit and it also ,was no good \\ I then checked all my wires.
5)Went back to the store and returned the gauge for another and it worked.

I checked my oil pressure with a gauge afterwards and it was 60psi at idle 1000rpms.
Most repair manuals say 55 pounds at 2000rpms.
MAKE SURE YOUR IDLE IS HIGH ENOUGH TO KEEP THE MOTOR RUNNING SMOOTH AT START UP.