Question is normal for a rear differential to get super hot after a 1 to 2 hrs highway trip of 80-85 MPH?

Warm is very normal. Super hot is very abnormal. There is a problem with the definition of the word "hot" from person to person. To me, "super hot" means it's smoking, and can not be touched. If you said it was 110° F, I would say its normal, but if you said it was 180° F, I would say it's not. A car engine generally runs around 180 to 195° F (or slightly hotter). Does the differential make any noises? Like a whining noise, or grinding noise? Is there a smell, like it's burning? Is fluid leaking out? If it has a leak (cover gasket, pinion seal, axle seal) and leaks out enough lubricant, it will run too hot and start making noises as damage starts. You can check the level of lubricant. There is a fill plug on the axle housing, maybe on the passenger side, about 6 inches behind the universal joint. If you take the plug out, you can carefully stick your little finger in the hole, when it's not HOT, and point your fingertip downward, and be able to touch the liquid. You should have lubricant on the end of your finger. If you don't, it's LOW! Find out what Chrysler recommends for the lubricant. Get a quart of it (has a tip on the container like a ketchup container in a restaurant) and squirt some in. Keep adding until you can get some on your finger. If you fill it and it starts coming out the hole, put the plug in. If you put the whole quart in, you need to get another quart and keep filling, but understand that you have a leak. It must be found and repaired. You could replace a leaky cover gasket. But if it's an axle seal, if you don't have somebody to show you how to do it, take it to a rear axle shop or general mechanic. If it's the pinion seal, do NOT attempt to do this yourself. That large nut that holds the u-joint flange on, MUST be tightened an exact amount, related to the thrust clearance in the pinion bearings. You don't just tighten it until it's "tight". You could ruin the pinion bearings in a short time, and maybe more. A pinion seal needs to be repaired by a dealership or rear axle specialty shop. A general mechanic is not qualified to do this properly, in most cases, in my opinion.

NO. Warm is all it should get. You have a bearing going out or it is out of adjustment, or if it has a limited slip differential, it is going out.

It is normal for it to get hot. However, define "super hot?"