2003 Tahoe oil pressure fluctuates then drops to zero 1/2 to 1 hour drive time. Replaced oil pressure sending unit and oil 5w30 with filter. Engine temp normal no knocking noises heard.:banghead:

Welcome to AF.
No noise is good.
What mileage?
What kind of oil filter are you using?
First thing you need to do is to get a manual oil pressure test gauge on it and give us the readings.

Thanks for having me, My Tahoe has 85,200 miles and I use mobil 1 synthetic oil 5w30 suv and mobil 1 synthetic oil filter. Would it be o.k. to go back to conventional oil? By the way owners manual says use 5w30 or 10w30 why can't a thicker oil be used with higher mileage engines? Thanks.:banghead:

Get a manual oil pressure gauge on it and see what the actual real oil pressure is.

85K is not high mileage.
If the book says use 5W-30 use it.

Why would you want to switch back to regular oil?
A lot of people like the synthetic oil.
And good engines just love it.
It is good stuff.
If you want to switch anything go to a AC Delco oil filter and see if it makes an difference in oil pressure.

Switching oil or switching ships in the middle of the ocean can cause problems sometimes.