Yeah Ive heard that among other things.
NV 3500 Silverado Gear Ratios:
1st: 4.02
2nd: 3.21
3rd: 1.49
4th: 1.00
5th: 0.73
The fist gear is impossibly low for a car. If you had a mild, 3.08 rear end, your first gear final drive ratio is 12.38. It's granny gear. You would have to shift before getting through an intersection. You basically wouldn't need to ever use first gear. Second is still pretty low for a car/hot rod. Look at the huge drop from second to third. If you have something with some cam in it, when you shift from second to third, the engine RPM's are going to drop way down out of the engine's power band and it's going to be a dog. For comparison, let's look at the gear ratios on a TKO600 (600 ft. lb. torque capacity).
1st: 2.87
2nd: 1.89
3rd: 1.28
4th: 1.00
5th: 0.82 or 0.64
If you have a 3.23 rear then your final drive ratio in first is 9.3 (3.23x2.87). 9-10 is where you want to be. With a 26" tall tire you would be turning 2738 rpm at 80 with the 0.82 overdrive. That's a little fast for my liking but being able to do 80-85 on the interstate here in Texas is a priority for me. With the same rear axle ratio and 26" tall tire, you would turn 2137 RPM at 80 with the 0.64 overdrive. That's more like it. With a 3.42, a 26" tall tire and the 0.64 overdrive, you would turn 2263 RPM at 80. That is how I would set it up. The 3.42 with the 2.87 first gives you a 9.8 final drive ratio in first.
Let's look at the LS1 T56 - torque capacity is said to be 450 ft. lbs.
Gear ratios: (typical 4th Gen F body)
1st: 2.66
2nd: 1.78
3rd: 1.30
4th: 1.00
5th: 0.74
6th: 0.50
You can see the high (numerically low) 1st gear and 6th gear will lend themselves to a fairly steep rear gear. With a 3.73 and a 26" tire, you would have a final drive ratio in 1st of 9.9 and would turn 1928 rpm in 6th at 80. You almost don't need 6th. I'm not crazy about how these trannys are geared.
Covette Z06/GTO T56 Gear Ratios:
1st: 2.97
2nd: 2.07
3rd: 1.43
4th: 1.00
5th: 0.84
6th: 0.56
The overdrive ratios are better on this one but 1st gear is a bit steep and there is a big drop from first to second. If you run a 3.42 and a 26" tall tire, your final drive ratio in 1st is 10.15 (slightly steep). You'd turn 1980 RPM in 6th at 80. Again, you don't really need 6th. You are limited by how much rear gear you can put in the car by the steep first gear.
Now for the best of both worlds....
T56 Magnum TUET-7477 - torque capacity 700 ft. lb.
1st: 2.66
2nd: 1.78
3rd: 1.30
4th: 1.00
5th: 0.80
6th: 0.63
This one has the first gear of the 4th gen F-body T56 but has lower (numerically higher) overdrive ratios. With a 3.42 you have a final drive ratio in 1st gear of 9.1. At 80 mph in 6th with a 26" tall tire you turn 2228 RPM. Set up this way, you only use 6th on the interstate but it is a usable gear. This is the transmission we have in my brother's Camaro. The downside to the TKO 600 and the T56 Magnum is cost. They weren't used in a production car so they are aftermarket only and are costly. The LS1 T56 is a little more affordable but there aren't that many out there. Getting a good deal on one that isn't thrashed is tough.
And now a look at a compromise:
91 IROC Z World Class T5 - Torque Capacity (315 ft. lbs.)
1st: 2.95
2nd: 1.94
3rd: 1.34
4th: 1.00
5th: 0.73
With a 3.08 rear end you have a final drive ratio of 9.1 in first gear. With a 26" tall tire you turn 2324 RPM at 80. It's a pretty well balanced setup. The drop from 1st to 2nd is a bit much but is manageable. Like I said, it's a compromise. The downside is torque capacity. This is what I'm putting behind my 350hp/400ft. lb. SBC. I won't be running slicks and won't be revving it to 5000 and dumping the clutch so I don't anticipate tearing it up. I'm using the 83 Camaro bellhousing that tilts the transmission over the way it was in the 3rd Gen F-body. The 83 Camaro bellhousing allows the use of a mechanical clutch linkage. It might have been less expensive to use an aftermarket hydraulic setup.
The trouble with converting these cars to a manual transmission is cost. The truck transmissions are appealing because they were relatively plentiful and are therefore less expensive. Unfortunately, they just aren't geared anywhere close to right. It's much easier and lese expensive to go automatic but for me, I have to have a stick in my hot rod.
I hope this discussion is helpful for you and others. I hope it helps folks get to where they want to be.