Have you tried swapping in your old oil pressure sender?
When you put the thread tape on the sender, did you block the tiny hole?
Is your truck still 24 volts? If you've converted to 12 volts you will need to remove and bypass the dropping resistors on the back of the cluster.
You may also have a gauge issue, it happens on older vehicles. You may fix the big problem, but its all the extra little ones that get you.
