the guy i bought my 5.0 from said that it has a 3.73 rear end and id like to be able to confirm it. is there an rpm chart i can refer to? if it helps, at 80mph im turning ~2700rpm
jack up the rear of your car and support it on jackstands. mark a rear tire with chalk,marker, ect and also make a mark on your driveline. count how many turns (by hand) of your driveline it takes to do one full rotation of your rear tire. this will tell you your ratio. 3.27:1, 3.55:1,3.73:1 ect. Charts can be deceiving as tire size differences aren't always accounted for. Hope this helps.
Make sure your speedo is correct too. You say you're doing 2700rpm @ 80mph, but gear swaps often result in inaccurate speedometer reading if care is not taken to put in the right speedo gear for the rear end/tire combo.