Q: The truck shakes and there's an imminent smell of gas but no signs of leakage. When accelerating it also backfires multiple times.

Hi there. If there is a smell of fuel in the engine compartment, then the fuel injector o-rings are not sealing and causing the smell of fuel to vapor out. The backfire event is caused by the ignition either being late or the timing is off. Check the spark plugs and wires to see if they are old. Old plugs and wires will cause an engine to backfire. Also, if the timing is off, then the engine will backfire. If you need further assistance with your engine backfiring and finding the fuel smell, then seek out a professional, such as one from Your Mechanic, to help you.