The turbo will have a distinct sound. Ours sounds almost like a police siren two blocks behind you. Putting a boost gauge in is the only real way to test it though. Might want to check the wastegate to make sure its not rusted in the closed position, that has been known to happen on these old rangers.

Your stalling problem may have been triggered by the biodiesel. Veggie oil has a powerful ability to clean all the deposites in the fuel system that may have been collecting for several years. This usually means that an engine that has never run on bio can quickly clog the fuel filter with all those stripped deposites. If it was sitting for a while, that would not help either. It can also eat rubber fuel lines and O rings, just a thought.