Thank you very much for your thoughtful and thorough replies @2001LC & @Julian Stead . First off, yes, the motor is a VVTi motor. To tell you the truth, I have not gone and inspected the other spark plugs as well as testing other coils. I've been focused simply on the 3 & 5 cylinders. I think it is indeed time to move in that direction. I'll go and inspect for any intake leaks at the manifold gasket. That is a good idea. I actually have a smoke machine, which I can attach to the TB and check for any leaks. As far as me mentioning that the AF sensors, I was more just checking that they were original Toyota's, appeared not to be replaced, and the truck having 150k on it. My main purpose of that statement was to question weather or not these sensors are good for 150k+ miles, or should I dive deeper into them. Also, from what I can find, the FSM only shows how to test the heater circuit but not the actual functionality of them? I've removed and had several injectors serviced through the years, obviously during head gasket jobs, and believe that is a good way forward as well. Thanks for the help, I'll continue to keep this thread updated for future reference.