It depends entirely upon the type of fuel you use. In your type of engine, the fuel must vaporize ( be volatile) and mix with air before it will ignite and produce power.
It is not designed to compress solid fuel until the fuel builds enough heat to ignite, like a diesel engine.
That means the fuel must be volatile like gasoline or alcohol, or already vaporized like natural gas, propane, or hydrogen.
Solid fuels that won't vaporize like vegetable oil will just clog the system and not ignite in the engine.
To use something like alcohol, all you need to do is change the fuel metering chip. The 2005 GMC is an alternative fuel vehicle meaning it will burn up to 20% Alcohol / Gasoline mixture without any changes. ( Check your Owners Manual ).
If you want to upset ATF, and set up a still in the wood shed and make your own alcohol and burn 100% alcohol, purchase a chip for 100% alcohol from your GM dealer.
To use Natural Gas, Propane, or Hydrogen, you will need an entirely different fuel intake system for your engine, and different wiring / O2 monitoring chips systems.