Oil pressure gauge reads high initially gradually moves completely past max

[StockMan]

Gauge on initial startup reads around 65lbs but shortly after that it begins to creep up to max (80lbs) and then after a driving a short distance it pins itselft.
I changed the sending unit and that seemed to bring things back to normal but shortly after the same thing again, where the gauge pins.  I plugged in my mechanical gauge and oil pressure is reading as it should (50lb idle and 65lb driving).

Other gauges seem ok.
Any ideas?  Ground?

Thanks

[HANDM]

Unreliable 50 year old gauges are the problem, at least in my car they are.
Oil pressure gauge sometimes stays at zero, or starts at 20 then moves to 40 moves again to 80 then settles back to 40 

[b5blue]

Replace the sender. 

[StockMan]

Thanks, I did replace the sending unit.  Maybe I'll try the 10ohm resistor in line and see if my gauge reads consistently up on full.
I'll have to see if I'm getting a decent connection as well, I had to splice the wire close to the sender as the clip fell off.

[b5blue]

Yea I meant replace the replacement. Like one from Tony's that your certain is correct. 

[OzCharger69]

I gave up on the stock cluster and have some Dakota gauges coming next week. It's cool to keep the old cluster functional but it's a pain in the arse to pull out everytime something goes wrong.

[StockMan]

Agree, I have it unhooked now, and because I have no time to take things apart I'll have to drive it like that for a while which really isn't optimal.
Flip side though I kept the car 100% original where I could so I'll have to suffer for now