If you're rpm is 2000 @ 50 mph, someone has probably replaced the stock 4.11 gear set with a 3.55 ratio.
You can play around with an
rpm calculator and see what you've got.
Vehicle speed comes up 50.3 mph if you plug in
2000 rpm, 1:1 transmission ratio, 3.55 gear ratio and 15" tire radius(not sure exactly what yours would be).
