I have replaced oil pressure sending unit

First have the actual pressure tested with a mechanical gauge to determine if it's a gauge problem or if the pressure is too high. If you really have 80 psi, I'd expect to see blue smoke from the tail pipe from too much oil on the cylinder walls overloading the oil control rings.

Did you replace the sending unit BECAUSE the pressure was reading so high, or did this start since the sending unit was replaced?

There was a lot of trouble in the '90s with the sending units causing fluctuating readings, especially at idle, so we did replace a lot of them. Also, there are different ones for different engines. The one I'm most familiar with is Chrysler's Mitsubishi 3.0L in the Caravans. On those it is acceptable to have only 6 psi at idle. That's way too low for most other engines. Their sending units are calibrated to keep the gauge reading in the "good" range at idle but that would result in a very high reading if it it was installed on other engines. If your high reading just started with the new sending unit, it sounds like you have one meant for a different engine or it was boxed wrong. Sometimes people check multiple parts at the parts store to match up a new part to their old one, then they put them back in the wrong boxes.