So, just a quick detail. 89 RS 305 converted to 350 last year, read the threads, did all the correct swaps and ran great for a year. This summer I swapped over from auto to t5. Everything went great for a week, drove it back and forth to work. I was on my way home from a cruise night, pushed the clutch in to downshift and it stalled. Wouldn't idle or run after that. It cooled down a bit and I nursed it home, barely. it seems to run a little better when cold but still won't idle. As it warms it starts coughing and skipping and barely running. I got a code 44. if I disconnect the MAP it runs smooth and will idle but will not run if I put a load on it. I can cruise around like this at low rpm's if I ease into the gas. I haved checked all the vacuum lines and connections on everything else. The cat is hollowed out so I know that isn't clogged. It has a new O2 sensor. I'm looking for help as to where i should start or go from here.

 

As you know a code 44 is O2 Lean signal at or below .2v for 20 seconds in closed loop.
For an exhaust leak to affect the O2 sensor it needs to be located somewhere between the head and sensor.
Disconnecting the MAP wouldn't make it run better if there's an exhaust leak.
Check fuel pressure, and add a bottle of HEET to gas tank in case there's some water in it.