Chevrolet,Does my vehicle have an oil pressure sender or oil pressure sensor or both and where is it located?

When truck gets to operating temp the oil pressure drops to 0-10 but jumps back to 40-60 while driving. There is no knocking or ticking and the oil level is good. My research points to the oil pressure sending unit or sensor. I would like to do the work myself but I do not have a pressure guage to check the pressure manually. I figured that I might replace one or both of the parts previously mentioned and if I can't track the problem then I will have to take it to a mechanic.

My car has 175000 miles.
My car has an automatic transmission.