The original Engine was a 305, but was switched out with a 350 Small block from a Chevy Truck.

This new engine has at most 70 K on it.
Here's my issues.
I just had the oil pump sending unit replaced, The Oil Pump itself replaced, put in a manual gauge, had the screen replaced because the old one was broken, dropped the pan, new oil Filter as well.
Now my gauge reads 55 psi as start up, then goes down to around 15 at idle, now it shows 15, but the shop tested this and said the gauge is off by about 7-8 ps1 so that means at Idle its running about 20 or a bit higher, now if I put it in park or neutral the gauge shows 20 psi which means its closer to 30. When I'm on the gas or on the freeway it shows around 35 to 50 psi.

Never drops to show lower then the 15 on the gauge, now I've had alot of work done, new carb, new Manifold, new plugs, wires etc... There is one fouled plug I cant get out.
today was the first day I drove it since I got it back and I drove it for almost 2 hours and everything was fine, then got home and it stalled out just as I got in.
There is no knocking, the pressure showed to be fine.
Any ideas??
Todays my birthday and I'm new to this so could someone help me out>?
Thanks in advance.

 

Welcome aboard thirdgen.org.

And, happy birthday.

Your oil pressure is completely normal.

Sounds like you need to get that one spark plug changed.

 

Thanks, also I seem to have more issues with the Holley 4 Barrel then my old stock Carb.
Its back loading a bit and my RPMs are dropping a tad too low when I idle and then I stall out.
Any suggestions?