or under strain. But if i shift into a lower gear, it seems to stop, for the most part. changed plugs, wires and timing chain around 100K.
Any advise would be appreciated.
Well many things can do that but you say if you shift it at a lower gear it doesn't seem to go as bad. So that's a problem that when you put it under load at lower rpms at box but then in a lower gear it doesn't. So either the transmission is starting to go out or you have a problem with fuel not being fed into the engine correctly at lower rpms like we feel injectors bad math sensor, vacuum leak
First off, do you have the 4 cylinder engine, or the 3.4 V6, because that doesn't have a timing chain?
I had a little issue like that, it could be described as bucking, in my 98 4Runner. It was a misfiring cylinder caused by a coil pack. I only seemed to get it in overdrive when going up hills, right before it would downshift. When I looked at the coil packs, I could see one with green corrosion on the "electrode?" in the coil pack that would be in contact with the spark plug. A new coil pack fixed it, although I may could have just cleaned it. Might want to check yours just in case.
Also, at that mileage, you should go ahead and change those plug wires for sure. I have had some fail as early as 35k miles, but the NGK I used always did great, but I changed them probably at 25k miles to be safe, besides they were cheap.
Unless you used platinum or iridium spark plugs, better to go ahead and replace those as well.
