my car was doing the same and when hooked to a computer it says that my alternator isnt putting enough voltage and therefore making my trans start off in a higher gear making me lose alot of power. it also said something about my quad something or other and that it was causing issues with my trans or something but there is nothing wrong with my trans.

There'* now way you're spinning the tires in 3rd gear, maybe if the shifter is in the "3" gate....

I'd keep doin gthe tuneup.