Ron,
I'm not familiar with the truxtell overdrive, so I don't know what the output ratio is. I suspect that with the 3.55 rear end, as discussed below, your final ratio might be too high to be practical except driving down hill or down wind.
As far as I know, the only ratio available for the 1940 1/2 ton rear end besides the stock 4.11 is the after-market 3.55 gear set that fits 1940-54 1/2 tons. Anything else would require changing the entire rear end.
I just finished installing a 3.55 ring and pinion set in my stock 1940 1/2 ton Chev pickup. I bought the gears from Mother Truckers in Arizona for $330.
So far, I've put about 300 miles on the gears, mostly on the open road, trying to get a feel for the new ratio.
I have a tachometer in my truck and with 6.00-16 tires and the stock 4.11 rear end, at 2500 rpm, the truck speed was 50 mph. With the 3.55 gears, which are 1.1577 times higher than the 4.11, the truck speed is 58 mph at 2500 rpm.
With the 3.55 gears, the truck cruises really nicely at 60 mph, with the stock 216 ticking over at about 2600 rpm. If your engine is in good shape, you could drive at 65 mph all day long if you wanted, with the engine running at 2800 rpm. At 70 mph the engine is turning about 3,000 rpm, which is nearing the upper end of where you'd want to run for extended periods.
I don't have any trouble getting up to and holding 70 mph unless there is considerable head or cross wind.
On a 240 mile test run at 60 mph, my gas mileage improved from 15.5 to 17.5, but I've only run one tank through, so those results could be an anomaly.
With the 3.55, you'll definitely feel the higher gears, and the truck will slow down on hills. Since there's about 15% difference between the 4.11 and 3.55 gears, I suppose it's like running with 15% less torque.
With the little testing I've done so far, the increased cruising speed capability outweighs the loss of torque on hills, and I'm quite pleased with the gear change, so far.
I do notice more driveline noise over the stock installation, and at first I thought it was from the pinion bearings because I installed the new gear set with used bearings (not recommended), but I subsequently took the unit apart and replaced the used bearings with new ones. The driveline noise remained the same, so I'm pretty certain the increased noise level is from the gears. The increased noise is not enough to discourage you from installing the 3.55 gears.
Patrick's, also of Arizona, sells the same gear set, and they also have an installation kit available that includes new pinion bearings, differential side bearings, a new pinion bearing retaining nut and shims and gaskets. The installation kit costs as much or more than the gear set.
I was pleased with the fit and finish of the gear set I bought, and the installation was pretty straight forward with no surprises.
I recommend the 3.55 gear set if you plan to do a lot of highway cruising. However, if you only drive around town, it's probably not worth the expense involved.
Mark
