And I run mine with a 3.07 rear end ratio. But hey...I'm a member of the Old Geezers Club so I get some special privileges, don't I? Kidding aside, I pitch in with Evan completely here (as I mentioned to another poster asking about this recently)...figure your cruise rpm to be around around your max torque rpm for efficiency. Once you eclipse efficiency and pass over to the other side, you can watch your gas consumption increase. 50+ years of driving these trucks has taught me that and it never varies.
As for the 3.07 and the T5, I've mentioned all this before but here is why it works: T5 with the gear ratio chain beginning with 4.03 first gear gives an overall ratio of 12.37 (a great first gear for a 1/2 ton pickup with an inline 6 and very close to the 12.08 OEM AD first gear ratio). Second and third gear overall ratios in this T5 will also match OEM within hairs, so in the first 3 speeds, your truck will seem just like a stock AD truck with a synchronized first gear. Then when you get to 4th, you get your first "overdrive" gear...a 25% drop in the overall ratio to 3.07. Is this reasonable? Yes, it is. Let's look: The old 3 speed with OD always came from the factory with the 4.11 rear end and then the overdrive dropped things 30%, so you're fine. If you had the old overdrive they mated with the 235, your final ratio would have been 2.87 (which is about 7% more liberal than my 4th gear ratio). When I go to fifth gear (a .86 reduction), my overall drops to 2.64...a wee bit more generous than the 3 speed with OD would have given me, but...I have 15 inch wheels and tires with a 26.8 inch diameter, so we need to divide the 2.64 by .95 to get the real ratio...2.78 (very close to the old OD final gear ratio). Admittedly if I'm in very hilly terrain or headwind, I will just leave it in 4th, but when things even out, I'm back in 5th. It is a see-saw...if you lug the 235 you'll also wreck the gas mileage and you won't be doing the engine any good, either.
If you have a 3.07 or 3.08 rear end and the T5 with the right gear ratio chain, I think you'll be very happy with the combination. You can load 800 pounds of firewood in the back and drive home without a problem. And you can zip along on the highway at 55 or 60 mph all day long. At 60, my engine is running about 2000 rpm. The 1959 version of the 235 (up through 1962) had a torque curve that started getting flat around 1600 rpm and stayed that way until nearly 2800 rpm.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
