Hi guys, this is one of my first post, I've been looking around here for a long time now. I'm a tech at a toyota dealer and I've already seen horrors like that, most of the time in the 3.0L. 2 years ago I made a test in one, I knew I was rebuiding it a couple of weeks later so I said, What do I have to loose? I added 1 litre of DEX and let the customer go with that. When I opened the engine, there was at least half of the amount of sludge than the first time I removed the valve cover. What I would do in your situation, I would add 1 litre of DEX, run the engine in neutral at 2500 RPM for 20 minutes. Drain everything, fill up with new engine oil less 1 liter, add 1 liter of DEX, drive for 1 or 2 days, drain everything again, fill up without DEX, drive for 2 or 3 days and check oil color, if it's black like charcoal, take everything again from the start.
Sure you can have debris giving you problems but your engine is already condamned. I think you should try to clean it ASAP!