Rough Running at Highway Speeds

[71enthusiast]

I need some help here.
Today I was headed out of town and when I hit about 55 my truck started running terrible. It sounded like a machine gun but if I put my foot in it, it would down shift, pop, and take off with no issue whatsoever only to return again after I let off.
So I kept going hoping it would stop but it never did. I came over a hill and let of the pedal and coasted and that was when the motor completely shut off and I ended up having to call a tow truck.
When I got it back to town I was able to start it up and drive it home like nothing even happened!

I haven't a clue what the issue is here. It runs fantastic around town and I can even put my foot into it with no problems.
I also feel that maybe it happens when the truck comes up to temp for a good while? Perhaps related to my O2s?

I am running a 2000 Lt1 from a suburban and the only codes that throw are the MIL light code and MAP sensor (Of which I've replaced and tested and still the code keeps throwing)
Also I have checked for vacuum leaks when diagnosing the MAP sensor. Found none.

Someone, anyone, tell me something so I can start somewhere...