Could be some truth in the the drivetrain hum. For the first time in a long time I started noticing quirks and signs of age on my 4Runner. There is a drivetrain/diff hum at about 70mph on light throttle, lift off, it goes away, returns as soon as it settles into overdrive, very faint but when you're Atype obsessive compulsive...... you need to crank up the tunes! The other item and I know its well documented on the 4th gens is weak brake life. I had the rotors turned and new pads fitted at about 45,000 as it starting shimmying to a stop, and at 65,000 its back and feeling a bit like sandpaper. That said, best frikkin vehicle I have ever owned, it scares me to think I will have to replace it one day and the next one may not give such good service. I also had a few teething issues, most annoying being the gearbox shuddering at around 40mph in 5th over drive like its hunting, it never fixed itself and the dealer claim 'normal', so I learned to drive around it. Secondly wobbling tires when cold, new Revos at 45,000 partly cured it but not completely. I also have some driveline shunt at stops, which is odd because you never hear of it on a V6. It just doesnt bother me that much any more because its 'normal'. Keep the 4Runner, and work on correcting the niggles. At worst you'll still have $18-$20k to put down against the next vehicle in 3-4yrs, not so with a Chevy.