When I did my TBI build on my 4.3 I ordered a bung that the fuel line bolts into and it bolts into the Injector pod. I forget what it cost me now but it sure makes checking the fuel pressure easy. You may also want to check the fuel pressure regulator, these are known to go out in time as well on these.
And your right it`s quite common to find the throttle body completely caked with carbon, mine was so bad it took long hours of soaking and a pick tool to get it all out. When the map sensors getting little or no vacuum due to the carbon needless to say it runs lousy.
I went back and located this: