FB331

Car:
1987 turbo rx7 has microtech lt10s

My problem with car:
Bought and drove car home on a ten hour trip. It performed fine aside from a slight vibration. Coolant and temp gauges worked fine and have on the dozen drives I've had it on. Today i was driving and from the time i started it the fuel read full when it was at a quarter (from what i remembered) but i didn't notice my bro did and didn't know different. I drove away with little warmup and when i looked 5 mins later it was at three quarters. I pulled in and stopped and opened the hood and felt around and the engine wasn't warm yet nor the rad. Confused and scared i cranked the defrost and slowly made my way back home. I hit the cluster a few times and it appeared everything returned to normal then went back to random then worked fine when i parked it. Another thing to add is the blower was at full blast but would fluctuate in speed and seemed like a power issue as when i would hit the power window switch for instance it would crank the speed back up. No other gauges were affected btw.

Question:

Knowing stock gauges suck i don't want to rely on them as i would prefer to put an aftermarket coolant gauge in the car but before i do want to figure out the issue im having. Hoping for the best i was thinking a failing alt might cause some issues or possibly bad grounds, being they would be easy solutions. At the worst some sort of wiring behind the dash. Although it could be the cluster as well.

Hoping someone else has had this problem or has heard of this before and could chip in.

Thanks, Corey