1990 Mustang GT Temperature Gauge and Transmission

i went to get my oil changed and the guy mentioned that i had low oil pressure, low battery voltage, and my water pump was leaking. i replaced the battery, volatge fixed. i replaced the water pump, still leaked, replaced the thermostat housing, no more leak. however, the temp guage stops just below red though i have full coolant. That's problem 1. i added another quart of oil to try to get the pressure up, didn't work. i read that maybe i should try cleaning the oil sending unit... if someone could help me find that, that'd be terrific. that's problem 2. now, today, i noticed that as i reached for my stereo, i could feel heat on my arm coming from the shifter boot. when this F150 ticked me off, and i gunned it around him, i got white smoke from the center console and had to back it off. that's problem 3... to sum up

1- overheating or guage?
2- low oil pressure or guage?
3- transmission or something else?

Any help would be greatly appreciated. Thanks in advance!