Funky burning plastic smell

Very likely it was some sound deadener/undercoat material applied either at the factory or port, burning off hot surfaces under the hood and along the tailpipe with your first long drive.

 

Only smell I had was the new car/engine smell when hot. I would just check under the hood, check your Oil level, and make sure all your fluids look good.

I don't think you have any issue, but a quick once over would be a good idea. I am sure it's all the newness breaking in smell...
Climbing to that elev puts a bigger drain on the engine thus more heat. New Brakes etc.....You stated it was just picked up days ago,
so just keep an eye and do a engine visual and check fluids just to be safe and peace of mind.

 

I have had the same kind of thing happen to me with another new Toyota (non-hybrid). Turned out to be paint getting hot (baked in) in areas on the engine and around the exhaust system. No problem.

I wouldn't worry about it, just keep your eye open for a warning light and shut it down it you get one. As Bob suggested check the fluid levels, oil and both coolant systems.

 

I had the same thing happen to me a while back and it dissipated quickly. I checked things and everything seemed fine. I'm not sure what it was, but it did not last long and has not reoccurred.

 

I've had this occur twice now climbing from 5900' to 7000' in power mode (car will be a month old on 27th) in about 7 miles. When I stop the car I get that faint smell in the cabin that I correlate with overheating or overheated brakes. I keep checking to make sure my parking brake is really turned off. Smell dissipates quickly and does come from engine (checked tonight). No warning lights.

Another Prius owner asked if I had noticed this with my 2006 and I said no. She said she had noticed it with her 2007 during the break in period. I'll check with the Service Department tomorrow just to be extra sure. Note: I've only drive about 260 miles in town because I am still waiting for the clear bra to be installed prior to driving any distance.

 

Sure it's not antifreeze? Almost all engines seem to weep a
tiny bit of antifreeze smell when under really high speed/load.
.
If you're willing to remove your cowl, check around the exhaust
header and cat-pipe for anything charred, though...
.
_H*