My 4Runner (240k) died on the highway the other day. I was driving along at 65 on cruise control when all of a sudden the RPMs shot up to about 6500. I immediately took off cruise and found that if I gave the truck any gas the RPMs again shot up through the roof and the engine was not transferring any power at all to the wheels or drivetrain. I had to coast over to the side of the road. When I stopped, the engine was still running and didn't really sound terrible, it was idling. I then put it in park and shut the rig off. I tried to start it again and it cranked, but would not turn over. Got out of the truck and looked underneath- quite a bit of oil (pretty positive it wasn't ATF fluid, pretty black, just had all the tranny fluid flushed and replaced a couple years ago, felt like oil) dripping down from the skid plate (it's an aftermarket plate, so I couldn't see exactly where it was coming from, but looked sort of near the oil pan area, about where the steering crosses the pan).

So I am not sure what happened or what the diagnosis will be, but I am thinking I am going to have to replace the engine, tranny, or both. I have put a lot into the rig- SS1.2, new steering rack & hoses, brake upgrade, and there is almost no rust- pretty cherry frame.

I have access to 3rd Gen donor vehicles rusted out but low mileage. Is it a big deal to swap in a 5 speed if I need a new tranny?

What do you guys think happened and since the frame and body are all good where would you go from here?

Thanks for any advice.

Sounds like tranny on first read yet first step is to lift it and start looking around at 'end' seals, both engine and tranny, one or the other failed. Luck and yeah I'd replace with a used toyo (not rebuilt crap) engine or tranny. Enjoy the Runner!