I presume your "funky" smell is coming from the catalytic convertor. it is either burning off carbon that doesn't get hot enough to burn at normal conditions or you have enough hydrocarbons getting into the cat to change the chemical activity. Also under full load oxides of nitrogen are heavily produced. This is refered to as NOx where x can be equal to 2 or 3, giving either NO, NO2 or NO3 (not sure if there is a NO). One of the two smells terrible. The other doesn't. NO3 is a few water droplets short of being Nitric Acid.
Another likely possibility is that your exhaust is getting any of a number of lubricants leaked onto it. They just accumulate untill you get them hot enough by such driving to start them burning.
Bosch Master, ASE Master, L1
33 years MB technician