Growl like noise at about 30 mph?

It's not your computer. There was a problem with the site that hosts this one.

The pinion factor is the setting that involves tire size and axle gear ratio. That is an adjustment, or setting, in the Transmission Computer that stays in memory. That's important so it isn't lost when the battery is disconnected. When you get a used computer from a salvage yard, you have no idea what setting had been chosen on the previous vehicle, so it must be checked and changed, if necessary. This is no different than what we did decades ago when buying a used transmission. It was standard practice to remove the speedometer gear, look at its color and / or number stamped on it, then, if it was different, we simply reused the gear from the old transmission. Today that job is a lot easier, but it requires a scanner to view and change the pinion factor.

As for your current setting, there's no way to know what it has been set at until you read it with the scanner. If you don't have a scanner, the dealer can make the adjustment, and most independent repair shops can do it too. Unfortunately, most shops need to charge quite a bit just to connect the scanner because by the time they get them paid for, they're in need of an expensive update. To help speed things up, have the axle gear ratio and tire size or outer circumference written down so the mechanic doesn't have to spend time finding that information.

The less expensive alternative is to pace your truck first with another vehicle and compare speedometer readings. If your speedometer reads the correct speed, there's no need to do anything with the pinion factor.

You're missing the point of the pinion factor. You said you didn't know if it was changed a few years ago when a different axle was installed. That means we don't know what it is set at now. If this job was being done in a shop, a standard part of the procedure would be to check what tire size and axle ratio are programmed in right now, and change either setting if they need to be updated. That entire programming process would take the better part of two minutes with time left over for a swig of coffee.

The new axle has no idea it's in a different truck, so there's nothing to do before driving it. If you don't have a scanner, just use a friend with another vehicle. Follow him at a specified speed, then see what your speedometer is reading. If it matches, you're done.

The VIN doesn't tell anything about the axle gear ratio. Mainly it includes the engine size, plant it was manufactured at, and model year. Chrysler used to use a metal plate riveted on under the hood, usually on the driver's side inner fender, that had all the details like paint codes, interior trim codes, and things like that. If you have that on your truck, the parts department people like it when owners put a sheet of paper on it, then rub a pencil over it to make a quick copy. They know how to decode that information. I'm almost positive the gear ratio is included on that plate, but you may not see it as the actual numbers. It may be in code form, such "A3T", or "GY79", or something like that, and you won't know which one of the many numbers refers to the axle ratio. Generally the numbers mean nothing to us without a way to decode them. You may find the decoding information in the original Chrysler service manual too, near the front of the book.

Trucks also used to have stickers in the glove box listing all the options on it. Those generally included those code numbers plus a description that we could understand.

It also used to be exciting to find the "build sheet" on older classic and muscle cars. There were multiples of those with one being stuffed under the rear seat cushion, above the metal springs. I don't know if they still do that or if they ever did that on trucks. There too, as I recall, you need a way to decode the numbers. Those sheets used to be used on the assembly line so workers knew which tires to install, which engine and transmission were going into it, which axle and which gear ratio, and even which pieces of chrome and other trim packages. I don't know how they handle that now.

The point I'm trying to make about the pinion factor is you only know it was set right if you know the truck's entire history from new. If you know no one else had their hands in it, and you have no reason to suspect someone changed the pinion factor, it should be as it was when shipped from the factory. That won't "self learn", or change on its own. The only way it can be wrong now is if the Transmission Computer was replaced with one with a different pinion factor, a previous owner had it changed, or if a dealer mechanic changed it to match a custom tire size. If you think it has never been changed since new, and the current axle is the same ratio as the original, there's nothing to discuss and nothing to worry about. Common sense says to be aware that you should at least verify the speedometer reads correctly so you don't get a speeding ticket. If you find you're holding up traffic, or blowing past everyone, when the speedometer says you're going the posted limit, that's when I'd be concerned. Of course that doesn't apply if you live in some larger cities where everyone goes 20 miles over the limit.

Concerns over the gear ratio takes a back seat to whether or not the noise is solved. I'm waiting to hear some good news about that.