New member with a confusing problem. My 1993 pathfinder idles fine but loses power and won't move when I put it in reverse or drive

[Beaujohnson]

It started about a month ago. I noticed it stated to lose power and burn 3 times more gas than usual. The throttle was very sluggish and it would take forever to get to 2000 rpms, then the rpms would suddenly shoot up to 4000 rpms and wants to stay there and not shift properly. I recently had the transmission rebuilt so I'm confident it isn't anything to do with that. As the weeks progressed it began losing more and more power until it finally stopped pulling its own weight even on a flat hard surface. I started by checking the maf sensor. I cleaned it and checked it for function. It seems to be fine. Next I cut off the catalytic converter and straight piped it. I checked the o2 sensor and it works. I cleaned it and replaced it. I then removed the throttle body and noticed an oily substance inside the plenum. I cleaned it all thoroughly and replaced the throttle position sensor. Nothing! I pulled the plugs and they were whitish in color which tells me it's running lean despite using 3xs times more fuel than it should. The number one cylinder plug had basically burned the metal completely off the top of the plug so I replaced all the plugs and wires. I replaced the distributor cap and rotor about 4 months ago. It should be good. Next is pulled off then erg valve, cleaned it and did a vacuum check and it's working. I cleaned it and put it back on. I then pulled the idle air control valve and cleaned it and checked its function and it works fine. I checked for vacuum leaks and couldn't locate one other than an exhaust leak where the exhaust manifold meets the pipe flare. At this point I began thinking I had a fuel pressure issue. I checked the fuel pump relay and it works. I replaced the fuel pump and filter. After that I started it and it was running like it should when I put it into gear. Thinking I'd fixed it finally I cut it off and went to bed. The next morning I started it and let it warm up and after 3 or 4 minutes it fell on its face again. I'm in the process of removing the upper intake plenum to get to the fuel pressure regulator and and as I pulled off a hose that runs from the bottom of the throttle body to a component on the back upper right side of the plenum next to the erg valve and idle air control valve. I'm not sure what this component is just yet, but I noticed a liquid in the hose that seemed greenish in color. Regardless, there shouldn't be liquid in this hose. I'm assuming it's a vacuum hose but not sure. It's not gas! At this point I'm feeling defeated. I am trying to a free  service manual online and while searching for it I ran across this forum. Any advice would be greatly appreciated. I'm at a loss right now for ideas.