T5 Five speed slant six 74 Dart Sport.

Dumb it down for me brother.
20 years ago i bought a 73 satellite with a swapped axle. the seller/ previous owner said that I shouldn't drive long distances at 80 mph because it was a 4.11 geared axle, and that it couldn't take it regularly (driving an hour south to jacksonville, fl) and back daily...