Why does my car start to shake when I go over like 65 mph?

Without more details or observations, shaking at higher speeds is typically caused by a tire out of balance. If the tires don't have matching tread, their different characteristics can cause the truck to pull to one side, vibrate, or pull during braking.

Not to worry. Those gauges are notoriously inaccurate and are just meant as a guide. The temperature gauge on my '88 grand Caravan just squeaks by the half-way mark while pulling an enclosed tandem axle trailer that's bigger than the van, to an old car show swap meet the weekend after the 4th of July when it's really hot outside. The electric radiator fan will be running even at highway speed but the engine doesn't overheat. In the winter, the gauge struggles to hit the one quarter mark, but the heater will burn me out if I let it. That goes to show that the gauge just gives a rough estimate of the actual temperature of the engine. If you look at the gauge in a different truck similar to yours, you'll see it reads differently too. The main thing you should watch for is if it suddenly reads much different. Otherwise, anything between one quarter and three quarters can be considered normal and acceptable.