I as my name says have a 73 GTO & I run 3:73's in the rear end. I've had them in there for about 20+ years now. I bought my car new with 3:08's . Out on the road the 3:08's were great, you could get out & go & my top end was some where around 140-150. I don't really know as I've only went as fast as I could once with it & it got me a ticket in 1975 going back to my ship when I was late getting back. The cop was really great & we had a long talk & he & the other cop had a good laugh about it. I ended up getting a warning ticket out of it. A few years later I switched to a 4 speed & hated the 3:08's in it then. I installed the 3:73's in it a years later & I love those gears. I get around 16 MPG running about 60 MPH. If I step it up from there the mileage goes down but not enough to want to go o a lower gear set. With the 3:73's & the 4 speed I run , it's an M-22. It comes out of the hole great & I run mid 11's in the 1/4 so I will keep them. Those gears are the best thing I have ever done for the car. I am running a 462 with Eldo. alum. heads & a RA IV cam 1:65 rockers, performer RPM intake & a Q-jet. The pistons are SRP forged with Eagle H-beam rods. I have RA IV exhaust manifolds to. I've had several different combos of engines in my 73 over the years but so far this set up works the best for me.