Having issues with my 87

My stang is running a little hotter than normal. I'm not exactly sure why because it has never done this before. It runs a little over the halfway mark on the temp gauge and before it always ran cooler then that.

A buddy of mine suggested it is because I'm running synthetic oil and that synthetic oil makes your engine run hotter. Is this true?? Should I not run synthetic on my stang???

Also my tach doesn't work for some reason. Someone suggested it could possibly be the ignition module but I've also heard it could just be a sensor that went out. Sorry for the dumb questions. Just learnin to work on it myself and any help would be appreciated.

When the engine idles, it runs at a pretty decent temperature. When I casually drive it is when it heats up to the mid point range (which I think is high)

When I'm fully throttled it heats up above the middle part of the gauge but doesn't overheat or anything.

I also noticed that sometimes my oil pressure fluctuates for no apparent reason. Sometimes when I have the vehicle throttled, the pressure seems low but still within the norm. Other times I'll be idling and the oil pressure will be low or sometimes perfect. Then there are times when I'm fully throttled and the pressure will be low or within the norm. I'm wondering if it's a sensor problem but I don't think it is because when the gauge shows the pressure at normal, the car (seems) to be running smoother which would make sense.