Brandon Todd

So I just got my 88 Sierra for a steal because the PO thought the engine was toast. The oil pressure gauge barely marks when the truck is running and sometimes it will go up just enough to shut the check gauges light off. But if you turn the lights or AC on the check gauges light comes on. And if you hit the turn signal the check gauges light blinks along with the signals. This is what brought me to the conclusion that the engine is fine but to make sure I manually tested the oil pressure and it is good. So now I have this truck and I am trying to figure out why it shakes between 35 and 45 MPH I've inspected the front end but I don't see anything that could be causing this. What should I be checking. Also the 4x4 only worked the first time I tried it. now it won't engage.