I noticed occasionally when I suddenly completely let off the gas I get this mild thump or sudden engine braking sensation. I also feel like I've been getting random RPM surges when driving at speed but it happens so fast and infrequently it's hard to catch it on the tach. And just now when I came to a stop on a hill and rolled back slightly the engine stalled which has got me worried now.

This is an odd one for sure. I would start with the basics, check your tranny fluid (low, old, burnt, overfilled etc).

This could be a lot of things. You'll have to explain in more detail.
Is the rpm surge accompanied by lack of acceleration. That would be transmission slippage.
Thump could be engine transmission mounts or flex plate.
As far as stalling on a hill (were you on gas or brakes)because if the selector is in the 'D' position and the car is moving backwards, on a steep enough hill to overcome the torque from the torque converter the engine will stall, due to the fact that the engine is forced to turn in the opposite direction to what it is actually doing.

It's hard to know exactly what you're feeling but a typical thump or clunk when letting off after the engine being under load is usually indicative of worn U joints in the driveshaft.

Ditto on greasing the U-joints, though that wouldn't cause it to stall out.

If you think it is the TC, check the color of the ATF. Does it look burnt? If you are climbing a hill under load, and the tranny shifts into OD (47mph+), will it bump then? There is a stall test to test it but I don't have the factory manual close by.

Normally the U-Joint that gives up the ghost first is the one nearest the rear diff. That would be my guess based on the thumping sound, but it doesn't indicate the other issues. A really bad U-joint feels like you are getting the back of your seat kicked by a mule every time you to to take off or let off the gas. lol.

sounds like a few issues. I agree with the warn u-joints, grease them up. The surging and stalling could also be MAF. Clean it and see if that improves.

What about torque converter? Mine gives a slight "thump" if I'm going over 50 and I very suddenly let off the gas completely. Only does it when the torque converter is locked up though so I always just thought it was that unlocking

surges....maf..throttle positon sensor, .throttle cables need adjustment, fuel filter, fuel pressure regulator, low alternator output this effecting electrical system, thus spark and fuel
clunk coming from back ...u joints, slip joint,the expensive cardon joint, bushings, shock mounts etc...list goes on...
all of which can also be attributed to a newer vehicle for the owner not familiar with their rig and a few cans of wrench lubricant.....beer
not saying that's you..im sure its more mechanical to the rig

I have a similar issue. I did a drain and fill on my transmission about 2 years ago. Every now and then when I come to a stop, it acts like it's in neutral. It will roll backwards, or not at all when I press on the gas. If I bump the throttle, it comes back around and is fine from then on. I figured that a solenoid was sticking in the trans or something. Fluid level is good. I also feel a bit of a thud when I'm over 60 and abruptly let off the throttle. I was thinking something with the torque converter myself. I've put about 30k miles on it since the drain and fill. I just quit worrying about it, and just always remember not to pull out into traffic without confirming the trans in engaged, so to speak.