I have a '13 maxima and it won't rev over 2500 rpm. Was driving to work this morning with the cruise on, started passing someone, and it started looseing speed and bucking. No check engine lights or anything. Is it limp mode for the trans, and if so, why?

throttle body issue, these cars are drive by wire. Meaning there is no throttle cable, it is like a bluetooth connection,

If you were traveling at highway speeds for a considerable amount of time then accelerated somewhat hard it is very likely you limped the trans. This happens when the trans temp gets too high. Could be a sign of a failing cvt or it could just be you pushed it too hard. How many miles do you have? What was the temp outside? Do you drive up lots of inclines? Ever change your cvt fluid? If not, you might consider doing so.

It's not wireless, there is a wired connection just not a mechanical throttle connected to it. It has a 0-5V signal with respect to the throttle pedal.

Does it rev past that in park? If not, it might be a MAF issue.

FSM refers to "limp mode" as fail safe.

If it were the TB (throttle body) it would not have bucked, just literally slowed to a crawl.

Or:

The 1st may not initially trigger an MIL, the 2 latter would have instantly.

i was driving with the cruise set at 75. stepped on it up to 80-85 and then it was like it lost all power. i ended up coasting down the shoulder at 30. no lights on the dash. so i started to merge back on and it would shutter hard at 2500 rpm's. it felt throttle related as in a certain pedal position. put it in park at work, tried to rev, it wouldnt go past 2500 still. shut it off, then back on, same thing. got in it after work, everything fine on the way to the dealer.
i live 30mi from work, 24 of it interstate. some bigger hills. car has 78,000miles, it was 45-50 degrees this morning. i have never changed the fluid, it was a rental car prior. dont know if that is something they would have done.

With 78k on a previous rental vehicle I would most certainly drain and refill the fluid ASAP! It was probably abused somewhat as rental. Keeping the fluid fresh can go a long way towards prolonging the life of the cvt.

So, a week ago my wife had the oil changed. The lube guy said bad air filter. She told him I would change it later. Fast forward to today, dealer called and said MAF us bad. Someone improperly installed the filter and it sucked debris into the MAF. $550 to fix it. The lube center is footing the bill. Thanks for all your suggestions.