You mean higher gearing. Lower would be 4.11 etc.
A carrier is the section inside the rear end that the ring gear mounts too. Carriers have a flange where the ring gear actually mounts and is thin or thick depending on the series of gear sets it's made for IE: 2-series, 3-series, 4-series. With a 3.73 ring & pinion your rear carrier is undoubtedly a 3-series carrier. I would say a 3.08 ring & pinion ratio is as high as a 3-series would go. I'm fairly sure the ring is a 8.50 inner diameter, same as the older camaro's. However, if you wanted to switch to a 2-series carrier to really slow the engine down at 60mph with the converter locked up, you can do that. My '97 4x4 has a 3:42 gear and I think that is a really good comprimise for still being able to pull a 4000lb boat, plus keep the engine rpm's at, or below 1500rpm @65mph.
Someone else might chime in that high gears are similar to pulling. On nice flat highways that gear would really work but, pulling a headwind or long incline, I think milage would suffer. Light cars, like my '85 325e BMW have a 2.76 rear end ratio and do really well. The in-line six has enough torque to pull it in all-around situations. I remember pickups in the late-seventies came out with 2.76 gears. I understand todays transmissions have very different ratios then the old turbo 350's did and the Vortec engine makes a bunch more torque at lower engine speeds. I guess if it were me, I wouldn't go higher then a 3.08. Just my opinion...