2000 Maxima hesitation under acceleration

Hello all.
I just signed up at this forum and am impressed by the volume of informed discussion going on. It's great.
That said, I hahve a problem with my 2000 Max that the dealer is having trouble dignosing.
I've had the Max since new (5 yrs) and it has 31000 miles on it. It has been great until this week. The trans is automatic and under hard acceleration in Drive or 2nd the revs go flat at around 4000 ... there's a confused hesitation for a second or two ... then there's a hard shift and the revs drop back to around 2000 and acceleration continues ...
The dealer says the diagnostic shows nothing's wrong ... they cleaned the throttle chamber and reset the throttle pressure and confirmed that the fuel pressure is ok ... but the problem persists.
The "service engine light" was on for about 30 minutes of driving time about 5,000 miles ago.
I searched the forum for "hesitation" and it seems there has been a lot of related discussion ... but nothing exactly specific to this experience.
Any comments will be appreciated. Thanks
Cheers to all

Our vq30de engines recommend/require (I'm not sure about 2000 and up) 91 octane gas. This could be a simple solution to your problem. Under acceleration with the lower octane gas, our knock sensors can and probably will detect ping in the engine, which is pretty bad. Cars are smart - they will see that there is something going on with the engine, and will try to adjust the ignition timing amoung other things. This results in a very jagged powerband, there's a dyno somewhere floating online for proof, but I can't get back to it. If you're not filling up with the good stuff, try it. It might be what you need.
Lou

I'm with BigLou on this one. Run the premium grade fuel and check for a knock sensor code.

~THT