I have a 1983 f150. When I first turn it on the oil pressure gauge reads pretty high. Then if I turn the heat on and let the pickup warm up for 10-15 minutes, the temperature gauge and the oil pressure gauge both go as high as possible. As soon as I turn the heat to the lowest setting, the temperature gauge goes to normal (about in the middle). After driving for a while without the heat the oil pressure gauge also goes back down to about the middle. Any thoughts on if it's actually over-heating and having high oil pressure or just some issue with the gauges?

 

That is almost definitely a gauge or sender issue. Oil pressure will be higher right after you start it on fast idle till it warms up, but not high enough to peg the gauge.