Nissan Repair: Transmission shifting, nissan maxima, pep boys

Question
I have a 2001 Nissan Maxima that is having a transmission problem.  It is an auto transmission.  When it is hot outside (usuall over 90 degrees) and running the AC the transmission fails to shift from 2nd to 3rd.  It kicks into neutral.  If you let off the gas it will lock back into 2nd.  It takes about 30-45 minutes of running for it to happen.  If you let it cool back down for around 15 minutes the transmission works fine.  It also seems to work fine as long as you don't run the AC, at least I can't reproduce the problem with the AC off.

We've been to a few places including the local Nissan dealer and they just shrug their shoulders pretty much.  When it is cooler there does not seem to be any problem at all.  I'm considering putting on an aftermarket transmission cooler kit for about $50 to see if it gets rid of the problem.  Any help would be greatly appreciated.
Thanks
Mark  

Answer
Mark,

The temperature sensor in the transmission is causing an over temperature in the transmission.  Be it real or otherwise, the computer still thinks there is a problem and it locks the transmission in second to keep from hurting the transmission.  You could try a Hayden 404 transmission cooler, I bought mine from Pep Boys for around $50 bucks and installed in in front of the condenser, in-line with the radiator cooler.  Feel the lines coming from the radiator and the cooler of the two is the one you tie into.  That would run the transmission cooler and possibly get your problem solved.  I say this since you have no problem with the airconditioner off.  Give it a try or find a dealer or speciality shop that understands Nissan transmissions.