]Hi boys ive bought a 5l v8 love it but when not accelerating oil pressure starts to drop and goes all the way to the bottom only after the car has been driven for 10 15 minutes plus. Any ideas would be a big help

Does it happen all the time? The oil pressure senders do go bad but for me that's only ever been intermittent.

Put some thicker oil in it,if the oil pressure rises then its just worn bearings,crank,oil pump,comes with a motor that's done some miles,clearances get larger over the years and oil pressure drops.
No big deal,if it runs fine otherwise then id wouldn't worry about it,or you could get a mechanical oil pressure gauge and screw it in where the sender goes and check it that way.
I just sold a 300000km eb v8 with only 20psi or less when driving and the motor was fine,made great power.