So I have a '94 Chevy truck with a bad radiator leak (which may be unrelated). Yesterday and today I pulled off of the highway and the street light on the exit was green meaning I didn't have to come to a complete stop. When I slowed down for the turn and put it into 2nd gear it was as if only one cylinder was firing. I basically had no acceleration except for an intermittent jolt forward, every second or so. I came to a full stop in the intersection and then was able to go forward in first gear and then it was like nothing happened except for the engine temperature was in the red.
I suspect it is entirely related to the radiator leak - it sounds from the description like your engine has massively overheated, probably resulting in the headgasket blowing...
Check under the oil cap, is it full of a mayonnaise-like sludge? Also check your coolant ( or what is left of it) for signs of oil. Either of those are a key sign of HG failure. As Bob's comment suggests, a lot of smoke is another likely symptom, usually white steam from coolant getting into the bores.
If that is the case, the next step is to do a compression test, which will likely confirm it, as there is a good chance that the loss of power is due to a loss of compression on several cylinders. In a healthy engine, all cylinders will show similar compression values, somewhere in the region of 150psi for a petrol/gasoline engine, more for a Diesel - a decent compression testing kit will show the ideal range on the dial.
If you're lucky, you won't have warped anything, although it is usually recommended to get the head(s) skimmed when doing a gasket change, especially after overheating. This simply takes a thin layer off the bottom of the head to ensure it is flat and true. I have seen engines sieze up completely after overheating, but it doesn't sound like yours got that bad.