breaking up at mid-high RPM

You didn't mention a tuning device like a "chip" or Tweecer, etc...

If the car is running with the stock EEC-IV then it is running with settings for a stock 302cid engine and not a 331cid. The 94-95 ECM is very touchy this way.

Hello Steve

Without knowing what all the past Pro Tuner messed with

You are kinda at a disadvantage

You mention fuel pressure and timing values

You would think he would have set your fuel and spark with the tables in
the pcm and if that is so ... logic reasoning would dictate setting the fuel
pressure at what ever is the OEM value and the same would be said for
the dizzy setting ... which I KNOW ... to be 10.

I then would look at the throttle body to see if the blade stop screw
is not too far out.

Then you might wanna take a look at the bleed screw, isc, iac, or what ever
you like to call it. Might wanna count the turns to seat it lightly so you have
a starting reference or you can put it back to its original positon if need be.

On a FMS 60 or 65 tb (loacated under a small rubber plug) it is usually in the
range of 1.5 to 2.5 turns out but that might not be correct with an
aftermarket tb

After those tb adjustments you would be wise to reset the pcm and give it
a while for the adaptive strategy to help you as much as it can

The VSS sensor can cause idle issues as well but check it for proper
operation before you spend the money on my say

Just a few things you could try without going inside the pcm

Grady