2001 4Runner Sport feels like it's going to stall...

[JackBlack]

I've got a 2001 4Runner Sport with 48,000 miles on it... it's been having problems lately once it warms up a bit and feels like it's going to stall, even though it never does.

Basically, the problem started after getting new tires put on about 2 months ago (I'm not mechanically inclined at all, so I don't know if this is just a coincidence). After 5 minutes or so of driving on the highway, the car loses all response to the accelerator being pressed. This happens when I'm feathering the gas pedal in traffic, and always at about 1500 RPM. The car feels extremely sluggish and doesn't respond when I press down on the gas... this usually lasts for about 3-4 seconds. It also makes very quiet revving sounds... sort of a "rrrrr... rrrrrr... rrrrrr" sound.

After 3-4 seconds of stomping on the gas pedal, the RPMS take off to about 4500 and then the car feels like it "catches" and starts to accelerate again.

I took it into the dealer once to have it looked at and they couldn't find anything (they only test drove it for 4 miles after I told them it has to warm up for a while first). During my drive to work this morning, it happened every few minutes for the entire half hour drive, and it's getting to be very unsafe.

Any ideas?

[JackBlack]

48 views and no ideas on what it might be? Anyone? Anyone?