[MrBeast]

Originally Posted by cal30_sniper

My truck started life as a 454/TH400/3.73 gear with 31" tires. In that configuration, I never had trouble maintaining highway speeds up to 80mph (lots of trips on I-10 out in West Texas). I don't know if I would recommend 4:11s at that kind of speed, but it was never an issue for me with the 3.73s. 65-70mph was simply a non-issue, that's what these trucks were originally designed for. Nobody worried about running these things 70-80mph when they were new, I don't see any reason you should now either.

I eventually swapped my TH400 for an NV4500. The overdrive is nice, especially at 70+ mph, but not necessary. I tow in overdrive, but you have to watch the heat, as it ramps up quicker than in direct drive. I really wouldn't recommend towing anything heavy in overdrive with an auto, even a 4L80e. With either trans, if you're towing something heavy enough to require running in direct drive, you really shouldn't be pushing faster than 65mph or so anyways, so the gearing is a non-issue at that point.

Unloaded, with the NV4500, the truck will easily do 85-90mph cruising. However, neither the state troopers or the gas mileage are very friendly at those speeds. Not to mention, the windnoise gets pretty intense above 70. As an aside, I noticed no measurable change in gas mileage driving 65mph between the TH400 and the NV4500. The overdrive allows the engine to spin slower, but it has to work harder. Gas mileage comes out in a wash as a result. Above 65, aerodynamics play a bigger role, and your gas mileage is going to suffer regardless of drivetrain combination.

The NV4500 I got came out of a 98 GM truck. The GM transmissions didn't have the 5th gear problems that the Dodge transmissions do. A GM 4WD NV4500 has the round pattern transfer case that will bolt right up to your existing round pattern 205. That would make a sweet setup.

That is interesting because with the NV4500 swap I saw my mileage at 70 mph go from 8mpg to 12, with a carbed motor!